[gnome-build-meta.wiki] Add instructions to upgrade and swtich to development branch

[Javier Jardón Cabezas <jjardon src gnome org>]

commit a3c3e439a5182ae5974ddd27c9836d27d9309293
Author: Javier Jardón Cabezas <javierjc1982 gmail com>
Date:   Fri Aug 27 21:24:01 2021 +0000

    Add instructions to upgrade and swtich to development branch

 Bootable-images-in-virtual-machines.md | 12 ++++++++++++
 1 file changed, 12 insertions(+)
---
diff --git a/Bootable-images-in-virtual-machines.md b/Bootable-images-in-virtual-machines.md
index 1d16aa0..0aab1cc 100644
--- a/Bootable-images-in-virtual-machines.md
+++ b/Bootable-images-in-virtual-machines.md
@@ -18,6 +18,18 @@ If GNOME Boxes does not have osinfo entry, if using an updated version of the os
 Create a virtual machine using an "Operating System Image
 File". Select `installer.iso` from the checkout directory.
 
+## Update from the terminal
+Use stock ostree commands:
+```
+ostree admin upgrade
+```
+
+## Switch to the development branch
+Open a terminal and type:
+```
+sudo ostree admin switch gnome-os:gnome-os/master/x86_64-devel
+```
+
 ## Updating with local OSTree
 
 Run helper script: `utils/update-local-repo.sh`. This will create a