hcloud_server: clarify further for usage of ssh_keys (#55713)

* hcloud_server: clarify further for usage of `ssh_keys`
* Make lowercase and drop plural on ssh_key description

lib/ansible/modules/cloud/hcloud/hcloud_server.py

@@ -46,7 +46,9 @@
         type: str
     ssh_keys:
         description:
-            - List of SSH Keys Names
+            - List of SSH key names
+            - The key names correspond to the SSH keys configured for your
+              Hetzner Cloud account access.
         type: list
     volumes:
         description:
@@ -117,7 +119,7 @@
     image: ubuntu-18.04
     location: fsn1
     ssh_keys:
-      - my-ssh-key
+      - me@myorganisation
     state: present
 
 - name: Resize an existing server