chore(keycloak): set keycloak hostname and header mode for proxy

roles/keycloak/README.md

@@ -3,3 +3,14 @@
 Ansible role for deploying keycloak, currently only supports docker.
 
 Migrated from `entropia.sso.keycloak`.
+
+## Required variables
+
+- `keycloak_database_password` - password for the database user
+- `keycloak_config_hostname` - public domain of the keycloak server
+
+## Database configuration
+
+- `keycloak_database_hostname` - hostname of the database server, defaults to `localhost`
+- `keycloak_database_username` - username to use when connecting to the database server, defaults to `keycloak`
+- `keycloak_database_database` - name of the database to use, defaults to `keycloak`