update README about supported OSes (#7608)

README.md

@@ -122,6 +122,8 @@ vagrant up
 - **Fedora CoreOS** (experimental: see [fcos Note](docs/fcos.md))
 - **openSUSE** Leap 15.x/Tumbleweed
 - **Oracle Linux** 7, 8 (experimental: [centos 8 notes](docs/centos8.md) apply)
+- **Alma Linux** 8 (experimental: [centos 8 notes](docs/centos8.md) apply)
+- **Amazon Linux 2** (experimental: see [amazon linux notes](docs/amazonlinux.md)
 
 Note: Upstart/SysV init based OS types are not supported.
 

docs/amazonlinux.md

+# Amazon Linux 2
+
+Amazon Linux is supported with docker,containerd and cri-o runtimes.
+
+**Note:** that Amazon Linux is not currently covered in kubespray CI and
+support for it is currently considered experimental.
+
+Amazon Linux 2, while derrived from the Redhat OS family, does not keep in
+sync with RHEL upstream like CentOS/AlmaLinux/Oracle Linux. In order to use
+Amazon Linux as the ansible host for your kubespray deployments you need to
+manually install `python3` and deploy ansible and kubespray dependencies in
+a python virtual environment or use the official kubespray containers.
+
+There are no special considerations for using Amazon Linux as the target OS
+for Kubespray deployments.