`master` is now `main`

[Stefan Monnier]

The default branch of both the `elpa.git` and `nongnu.git` repositories
has been changed to `main`.  The old `master` branches have been
replaced by placeholders pointing to the new branch.

People who clone the repository anew should not be noticeably affected,
but for those who already have a clone, you'll have to switch to the
new branch.

For `nongnu.git` the new branch is a "fast-forward" of the old branch,
so all it takes is:

    git branch -set-upstream-to=origin/main
    git merge

For `elpa.git` OTOH the new branch doesn't share any history with the
new one, so you'll need something like:

    git checkout -b main origin/main

If you have local changes, you'll want to `git stash` before doing that
and `git stash pop` afterwards and it will likely give you non-trivial
conflicts to resolve.  Don't hesitate to ask if you need help resolving
such conflicts.

Note also that the new branch uses new code, so you'll need to do one

    make

as a first step (to fetch the scripts and setup the real makefile) and
after that it should work more or less as before, but you'll likely see
various differences.  I'm still working on improving those new scripts,
so if you encounter any particular problem/regression please holler:
there's a good chance I'm already aware of it, but it'll help me focus
on the cases that matter.


        Stefan