org-capture.el: Add :tree-type 'month' in org-capture-templates description

* lisp/org-capture.el (org-capture-templates): Enhance description and
add 'month' value for :tree-type in description.

* doc/org-manual.org: Fix typo for displaying 'month' in :tree-type
property.

TINYCHANGE

doc/org-manual.org

@@ -7722,7 +7722,7 @@ Now lets look at the elements of a template definition.  Each entry in
 
     Use ~week~ to make a week tree instead of the month-day tree,
     i.e., place the headings for each day under a heading with the
-    current ISO week.  Use @code{month} to group entries by month
+    current ISO week.  Use ~month~ to group entries by month
     only.  Default is to group entries by day.
 
   - ~:unnarrowed~ ::

lisp/org-capture.el

@@ -270,7 +270,9 @@ properties are:
  :time-prompt        Prompt for a date/time to be used for date/week trees
                      and when filling the template.
 
- :tree-type          When `week', make a week tree instead of the month tree.
+ :tree-type          When `week', make a week tree instead of the month-day
+                     tree.  When `month', make a month tree instead of the
+                     month-day tree.
 
  :unnarrowed         Do not narrow the target buffer, simply show the
                      full buffer.  Default is to narrow it so that you