add link to heyu group vars in readme

roles/heyu/README.md

@@ -19,7 +19,7 @@ Role Variables
 
 `heyu_version`: [semver](https://semver.org) of heyu. Ex: `"2.10.1"`
 
-### Other variables (set in host/group vars):
+### Other variables (set in [group vars](https://git.shareunderware.com/blaine/infra/src/master/group_vars/heyu.yml)):
 
 #### `heyu_aliases`: