perldelta: Move the XIDStart change from bugs to incompat.

and reword it.

This is probably not the best wording. If someone else is actually
reading this, please feel free to improve it.

pod/perldelta.pod

@@ -793,6 +793,12 @@ If it is absolutely necessary to have empty attribute lists (for example,
 because of a code generator) then avoid the error by adding a space before
 the C<=>.
 
+=head3 Change in the parsing of identifiers
+
+Characters outside the Unicode "XIDStart" set are no longer allowed at the
+beginning of an identifier.  This affects that certain accents and marks
+that normally follow an alphabetic character.
+
 =head2 Threads and Processes
 
 =head3 Directory handles not copied to threads
@@ -3544,12 +3550,6 @@ such as U+387 [perl #74022].
 
 =item *
 
-Several contexts no longer allow a Unicode character to begin a word
-that should never begin words, for an example an accent that must follow
-another character previously could precede all other characters.
-
-=item *
-
 Defining a constant with the same name as one of perl's special blocks
 (e.g., INIT) stopped working in 5.12.0, but has now been fixed
 [perl #78634].