[doc] Update Ubuntu to 22.04
This updates documentation to reflect the switch to
Ubuntu 22.04 (jammy) in the CI:
https://review.opendev.org/c/openstack/devstack/+/860795
Change-Id: I8bee430029dcc719629bd92451c2791571f8a30c
diff --git a/doc/source/index.rst b/doc/source/index.rst
index ba53c6d..3f206f4 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -40,7 +40,7 @@
attempts to support the two latest LTS releases of Ubuntu, the
latest/current Fedora version, CentOS/RHEL/Rocky Linux 9 and OpenSUSE.
-If you do not have a preference, Ubuntu 20.04 (Focal Fossa) is the
+If you do not have a preference, Ubuntu 22.04 (Jammy) is the
most tested, and will probably go the smoothest.
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