runtime(nroff,groff): update commentstyle in filetype plugins

closes: #17516

Signed-off-by: jtmr05 <62111562+jtmr05@users.noreply.github.com>
Signed-off-by: Eisuke Kawashima <e-kwsm@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/ftplugin/groff.vim b/runtime/ftplugin/groff.vim
index 3ebfa03..f628525 100644
--- a/runtime/ftplugin/groff.vim
+++ b/runtime/ftplugin/groff.vim
@@ -2,6 +2,7 @@
 " Language:  groff(7)
 " Maintainer: Eisuke Kawashima ( e.kawaschima+vim AT gmail.com )
 " Last Change: 2025 Apr 24
+" 2025 Jun 18 by Vim Project: update commentstring option (#17516)
 
 if exists('b:did_ftplugin')
   finish
@@ -11,5 +12,8 @@
 
 runtime! ftplugin/nroff.vim
 
+setlocal commentstring=\\#\ %s
+setlocal comments=:\\#,:.\\\",:\\\",:'\\\",:'''
+
 let b:undo_ftplugin .= '| unlet! b:nroff_is_groff'
 let b:did_ftplugin = 1