Note that `rsync` must be installed on both local & remote machine

In particular, if `rsync` is not installed on the remote machine the following error message will be encountered:

    "rsync error: remote command not found"

lib/ansible/modules/files/synchronize.py

@@ -145,6 +145,7 @@ options:
     required: false
     version_added: "1.6"
 notes:
+   - `rsync` must be installed on both the local and remote machine.
    - Inspect the verbose output to validate the destination user/host/path
      are what was expected.
    - The remote user for the dest path will always be the remote_user, not