Allow any vimeo.com subdomain for embeds.

props danielbachhuber.
fixes #24170.

Built from https://develop.svn.wordpress.org/trunk@27225


git-svn-id: http://core.svn.wordpress.org/trunk@27082 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Embolden some instructions when installing a network.

props Ipstenu.
fixes #27057.

Built from https://develop.svn.wordpress.org/trunk@27226


git-svn-id: http://core.svn.wordpress.org/trunk@27083 1a063a9b-81f0-0310-95a4-ce76da25c4cd