install: fix git error and support Ubuntu 22.04

refs #5204

Change-Id: Ic6e2ce789746a18cdb8b97e5a4e8175a89ad2e8d
diff --git a/docs/install.rst b/docs/install.rst
index 1697699..cd66d68 100644
--- a/docs/install.rst
+++ b/docs/install.rst
@@ -7,6 +7,7 @@
 Mini-NDN is tested on the following Linux distributions:
 
 - Ubuntu 20.04 (recommended)
+- Ubuntu 22.04
 - Debian 11 (WiFi scenario does not work)
 - Fedora 33 (WiFi scenario does not work)