org-capture.el: Document what the time stamp is in capture templates

* lisp/org-capture.el (org-capture-templates): Make explicit that the time
stamp aware %-escapes are influenced by `org-capture-use-agenda-date'.

TINYCHANGE

lisp/org-capture.el

@@ -242,8 +242,10 @@ be replaced with content and expanded:
               happens after expanding non-interactive %-escapes, those can
               be used to fill the expression.
   %<...>      The result of format-time-string on the ... format specification.
-  %t          Time stamp, date only.
-  %T          Time stamp with date and time.
+  %t          Time stamp, date only.  The time stamp is the current time,
+              except when called from agendas with `\\[org-agenda-capture]' or
+              with `org-capture-use-agenda-date' set.
+  %T          Time stamp as above, with date and time.
   %u, %U      Like the above, but inactive time stamps.
   %i          Initial content, copied from the active region.  If %i is
               indented, the entire inserted text will be indented as well.
@@ -261,7 +263,8 @@ be replaced with content and expanded:
   %^g         Prompt for tags, with completion on tags in target file.
   %^G         Prompt for tags, with completion on all tags in all agenda files.
   %^t         Like %t, but prompt for date.  Similarly %^T, %^u, %^U.
-              You may define a prompt like: %^{Please specify birthday}t
+              You may define a prompt like: %^{Please specify birthday}t.
+              The default date is that of %t, see above.
   %^C         Interactive selection of which kill or clip to use.
   %^L         Like %^C, but insert as link.
   %^{prop}p   Prompt the user for a value for property `prop'.