add install instructions to readme

README.md

@@ -106,6 +106,14 @@ We disable the following filesystems, because they're most likely not used:
 
 To prevent some of the filesystems from being disabled, add them to the `os_filesystem_whitelist` variable.
 
+## Installation
+
+Install the role with ansible-galaxy:
+
+```
+ansible-galaxy install dev-sec.os-hardening
+```
+
 ## Example Playbook
 
 ```yaml