Amplify the muddle doc docstring a bit
This just duplicates some of test_upstream so far...

...but it has different ambitions
Fixing subdomain support, testing various things

When doing a "muddle init" with subdomains and a toplevel "following"
build description, "sync" the subdomain build descriptions at the
end of the "muddle init" (which is the only feasible place to do this).

Cope with checkouts that are not checked out (well, can't find their
current branch) in "muddle query checkout-branches" - this allows
using it just after "muddle init", for instance.

Add tests for a "following" build description with subdomains,
and some testing for remote/upstream repositories still working
as they should (both in test_lifecycle2.py)
Ah - check not following subdomains
Create maintenance branch
Create maintenance branch
Add support for the "no_follow" VCS option

and consequently amend how VCS options are stored and handled.
Also report location of file for "muddle doc"
Fix small problem in muddle sync
Move lifecycle text to docs

..and work on it a bit