gnome-3-0 branch in gnome-user-docs

[Shaun McCance <shaunm gnome org>]

There's a gnome-3-0 branch in gnome-user-docs. Andre asked me
to send an explanation about this, since it's clearly not the
normal stable branching strategy.

This branch is going to be a hotbed of edits and re-edits and
thoroughly unstable content as we transition to Mallard. The
docs teams decided to do this on a branch to avoid massive
churn for translators. When the dust starts to settle, we'll
merge this back into master.

I'll also be creating the standard stable branch for 2.30.

Thanks,
Shaun