docs: Add README section for default branch

We are about to change it, so briefly outline how to update local
checkouts.

(Copied from glib)

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1914>

diff --git a/README.md b/README.md
index 7420bc3ac82894340ac4a8e9a056e70e9e85d653..523ff3ad7c02e2e308f41f383e8873d1fb8aa086 100644 (file)
--- a/README.md
+++ b/README.md
@@ -20,6 +20,19 @@ Commit messages should follow the [GNOME commit message
 guidelines](https://wiki.gnome.org/Git/CommitMessages). We require an URL
 to either an issue or a merge request in each commit.
 
+## Default branch
+
+The default development branch is `main`. If you still have a local
+checkout under the old name, use:
+```sh
+git checkout master
+git branch -m master main
+git fetch
+git branch --unset-upstream
+git branch -u origin/main
+git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/main
+```
+
 ## License
 GNOME Shell is distributed under the terms of the GNU General Public License,
 version 2 or later. See the [COPYING][license] file for details.