[devhelp/main: 1/2] docs: Mention the switch of the default branch name

[Emmanuele Bassi <ebassi src gnome org>]

commit 44c39c4cd0e80652600c4effbaa0e5a215404cdd
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Sat Jul 10 15:47:50 2021 +0100

    docs: Mention the switch of the default branch name
    
    Document that we switched to `main`, and add instructions on how to
    switch extant local checkouts.

 README.md | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)
---
diff --git a/README.md b/README.md
index c3c3595b..be0d57ba 100644
--- a/README.md
+++ b/README.md
@@ -62,3 +62,20 @@ Other documentation
 
 - There is an API reference manual for the libdevhelp that can be built with
   GTK-Doc, see the `gtk_doc` build option.
+
+Default development branch
+--------------------------
+
+The default development branch of Devhelp has been renamed to `main`. If you
+have just cloned the Devhelp repository, you don't need to change anything.
+If you have an older local checkout, you can use these commands to switch
+from the old default branch name to the new one:
+
+```
+git switch 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
+```