Belatedly update the releng/index.html page to note that
the stable/10 branch is frozen for the 10.1-RELEASE cycle.

Approved by:	re (implicit)
Sponsored by:	The FreeBSD Foundation


git-svn-id: svn+ssh://svn.freebsd.org/doc/head@45595 c2e8774f-c49f-e111-b436-862b2bbc8956