Add release note and upgrade docs for Ubuntu Focal 20.04

Change-Id: I439e8afc87d21aa8b7f381534c963e39f69c5d73

doc/source/user/operating-kolla.rst

@@ -64,6 +64,14 @@ Limitations and Recommendations
    ``"yes"``, you need to have the ``log_bin_trust_function_creators`` set to
    ``1`` by your database administrator before performing the upgrade.
 
+Ubuntu Focal 20.04
+------------------
+
+The Victoria release adds support for Ubuntu Focal 20.04 as a host operating
+system. Ubuntu users upgrading from Ussuri should first upgrade OpenStack
+containers to Victoria, which uses the Ubuntu Focal 20.04 base container image.
+Hosts should then be upgraded to Ubuntu Focal 20.04.
+
 Preparation
 -----------
 

releasenotes/notes/ubuntu-focal-bdc157d4505f9a0c.yaml

+---
+upgrade:
+  - |
+    Adds support for Ubuntu Focal 20.04 as a host operating system. Ubuntu
+    users upgrading from Ussuri should first upgrade OpenStack containers to
+    Victoria, which uses the Ubuntu Focal 20.04 base container image. Hosts
+    should then be upgraded to Ubuntu Focal 20.04.