Merge from origin/emacs-27

7be160d800 Improve "Help Summary" section in user manual
f6d6ccc984 Clarify message-sendmail-extra-arguments docstring
95fde1a851 * src/editfns.c (Fformat): Small documentation fix.

diff --cc doc/emacs/help.texi
Simple merge

diff --cc lisp/gnus/message.el
Simple merge

diff --cc src/editfns.c
Simple merge