fixed mcedit.1.in

Signed-off-by: Ilia Maslakov <il.smind@gmail.com>

doc/man/mcedit.1.in

@@ -496,6 +496,10 @@ save file position on exit.
 .I source_codepage
 symbol representation of codepage name for file (i.e. CP1251, ~ \- default).
 .TP
+.I editor_group_undo
+do UNDO for several of the same type of action (inserting/overwriting,
+deleting, navigating, typing)
+.TP
 .I editor_wordcompletion_collect_entire_file
 Search autocomplete candidates in entire of file or just from
 begin of file to cursor position (0)