add ceph install requirements to readme

Signed-off-by: Markus Katharina Brechtel <[email protected]>

README.md

@@ -9,6 +9,10 @@ Install incus stable or LTS on your system from the [zabbly/incus](https://githu
 
 Install [OpenTofu](https://opentofu.org/docs/intro/install/).
 
+Install the required ceph packages for ansible on the controller, on Debian that's the `ceph-base` and `ceph-common` packages:
+```
+apt install --no-install-recommends ceph-base ceph-common
+```
 
 ### Create the test VMs with OpenTofu
 Go to terraform directory: