added note about behaviour change in 2.2

system/known_hosts.py

@@ -23,9 +23,10 @@ DOCUMENTATION = '''
 module: known_hosts
 short_description: Add or remove a host from the C(known_hosts) file
 description:
-   - The M(known_hosts) module lets you add or remove a host keys from the C(known_hosts) file. Multiple entries per host are allowed, but only one for each key type supported by ssh.
-     This is useful if you're going to want to use the M(git) module over ssh, for example. 
-     If you have a very large number of host keys to manage, you will find the M(template) module more useful.
+   - The M(known_hosts) module lets you add or remove a host keys from the C(known_hosts) file.
+   - Starting at Ansible 2.2, multiple entries per host are allowed, but only one for each key type supported by ssh.
+     This is useful if you're going to want to use the M(git) module over ssh, for example.
+   - If you have a very large number of host keys to manage, you will find the M(template) module more useful.
 version_added: "1.9"
 options:
   name: