org-element.el: Encourage bug reports in case of cache issues

* lisp/org-element.el (org-element--cache-remove,
org-element--cache-sync, org-element--cache-process-request,
org-element--parse-to, org-element--cache-for-removal,
org-element--cache-verify-element, org-element-at-point): Update
warning messages.

lisp/org-element.el

@@ -5717,7 +5717,8 @@ Assume ELEMENT belongs to cache and that a cache is active."
       (progn
         ;; This should not happen, but if it is, would be better to know
         ;; where it happens.
-        (org-element--cache-warn "Failed to delete %S element in %S at %S. The element cache key was %S."
+        (org-element--cache-warn "Failed to delete %S element in %S at %S. The element cache key was %S.
+If this warning appears regularly, please report it to Org mode mailing list (M-x org-submit-bug-report)."
                       (org-element-type element)
                       (current-buffer)
                       (org-element-property :begin element)
@@ -5803,7 +5804,9 @@ updated before current modification are actually submitted."
       (if (/= org-element--cache-change-tic
              (buffer-chars-modified-tick))
           (progn
-            (org-element--cache-warn "Unregistered buffer modifications detected. Resetting\n The buffer is: %s\n Current command: %S"
+            (org-element--cache-warn "Unregistered buffer modifications detected. Resetting.
+If this warning appears regularly, please report it to Org mode mailing list (M-x org-submit-bug-report).
+The buffer is: %s\n Current command: %S"
                           (buffer-name (current-buffer))
                           this-command)
             (org-element-cache-reset))
@@ -6153,7 +6156,7 @@ request."
                          ;; such error happens within
                          ;; `org-element--cache-process-request' or somewhere
                          ;; else.
-                         (org-element--cache-warn "Added org-data parent to non-headline element: %S" data)
+                         (org-element--cache-warn "Added org-data parent to non-headline element: %S\nIf this warning appears regularly, please report it to Org mode mailing list (M-x org-submit-bug-report)." data)
                          (org-element-cache-reset)
                          (throw 'quit t))
 		       (org-element-put-property data :parent parent)
@@ -6222,7 +6225,8 @@ the process stopped before finding the expected result."
           ;; file.
           ((and (not cached) (org-element--cache-active-p))
            (setq element (org-element-org-data-parser))
-           (unless (org-element-property :begin element) (org-element--cache-warn "Error parsing org-data. Got %S" element))
+           (unless (org-element-property :begin element)
+             (org-element--cache-warn "Error parsing org-data. Got %S\nPlease report to Org mode mailing list (M-x org-submit-bug-report)." element))
            (org-element--cache-log-message "Nothing in cache. Adding org-data: %S"
                                 (org-element--format-element element))
            (org-element--cache-put element)
@@ -6604,7 +6608,7 @@ known element in cache (it may start after END)."
 	      (when robust-flag (setq robust-flag nil))))
           (unless (or (org-element-property :parent up)
                       (eq 'org-data (org-element-type up)))
-            (org-element--cache-warn "Got element without parent.\n%S" up))
+            (org-element--cache-warn "Got element without parent. Please report it to Org mode mailing list (M-x org-submit-bug-report).\n%S" up))
 	  (setq up (org-element-property :parent up)))
         ;; We're at top level element containing ELEMENT: if it's
         ;; altered by buffer modifications, it is first element in
@@ -6784,7 +6788,9 @@ Return non-nil when verification failed."
         (org-element-with-disabled-cache (org-up-heading-or-point-min))
         (unless (or (= (point) (org-element-property :begin (org-element-property :parent element)))
                     (eq (point) (point-min)))
-          (org-element--cache-warn "Cached element has wrong parent in %s. Resetting.\n The element is: %S\n The parent is: %S\n The real parent is: %S"
+          (org-element--cache-warn "Cached element has wrong parent in %s. Resetting.
+If this warning appears regularly, please report it to Org mode mailing list (M-x org-submit-bug-report).
+The element is: %S\n The parent is: %S\n The real parent is: %S"
                         (buffer-name (current-buffer))
                         (org-element--format-element element)
                         (org-element--format-element (org-element-property :parent element))
@@ -6810,7 +6816,9 @@ Return non-nil when verification failed."
                      (eq (org-element-property :contents-end real-element) (org-element-property :contents-end element))
                      (or (not (org-element-property :ID real-element))
                          (string= (org-element-property :ID real-element) (org-element-property :ID element))))
-          (org-element--cache-warn "(%S) Cached element is incorrect in %s. (Cache tic up to date: %S) Resetting.\n The element is: %S\n The real element is: %S\n Cache around :begin:\n%S\n%S\n%S"
+          (org-element--cache-warn "(%S) Cached element is incorrect in %s. (Cache tic up to date: %S) Resetting.
+If this warning appears regularly, please report it to Org mode mailing list (M-x org-submit-bug-report).
+The element is: %S\n The real element is: %S\n Cache around :begin:\n%S\n%S\n%S"
                         this-command
                         (buffer-name (current-buffer))
                         (if (/= org-element--cache-change-tic
@@ -7369,7 +7377,7 @@ element ending there."
                     (condition-case err
                         (org-element--parse-to pom)
                       (error
-                       (org-element--cache-warn "Cache corruption detected in %s. Resetting.\n The error was: %S"
+                       (org-element--cache-warn "Cache corruption detected in %s. Resetting.\n The error was: %S\n Please report this to Org mode mailing list (M-x org-submit-bug-report)."
                                      (buffer-name (current-buffer))
                                      err)
                        (org-element-cache-reset)