Minor tweak to the page on submitting docs updates

[Radio młodych bandytów]

http://www.freebsd.org/docproj/submitting.html

"Then post a message to the FreeBSD-doc mailing list, with a brief 
outline of the documentation and the pointer to its location, and 
solicit feedback."

It would be nice to add an URL to FreeBSD-doc. It would make it easier 
for noobs like me who don't know where to look for FreeBSD mailing lists.

-- 
Twoje radio