[glib: 5/6] docs: Add a section to the README about the branch rename

[Philip Withnall <pwithnall src gnome org>]

commit d81165216d97123aa01f902a716ab8338ee5ee76
Author: Philip Withnall <pwithnall endlessos org>
Date:   Mon Jun 7 13:26:46 2021 +0100

    docs: Add a section to the README about the branch rename
    
    Signed-off-by: Philip Withnall <pwithnall endlessos org>
    
    Helps: #2348

 README.md | 13 +++++++++++++
 1 file changed, 13 insertions(+)
---
diff --git a/README.md b/README.md
index 9ef3b3d6b..c53dd6f4d 100644
--- a/README.md
+++ b/README.md
@@ -47,3 +47,16 @@ Closes: #123
 
 Otherwise, create a new merge request that introduces the change, filing a
 separate issue is not required.
+
+## Default branch renamed to `main`
+
+The default development branch of GLib has been renamed to `main`. To update
+your local checkout, 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
+```