Add documentation and new healthcheck

.env.sample

@@ -6,6 +6,7 @@ REGISTRY_DOMAIN=registry.gitlab.example.com
 # The Gitlab Pages domain must not be a subdomain of the main Gitlab domain
 PAGES_DOMAIN=pages.example.com
 
+# Prevent public signups
 POST_DEPLOY_CMDS=disable_signups
 
 ## Domain aliases
@@ -26,4 +27,4 @@ SSO=false
 # ORG_NAME="My Organization"
 # SSO_PROVIDER_URL="https://authentik.mydomain.com/application/o/gitlab/"
 # SSO_PROVIDER_ID="your authentik Client ID"
-# SECRET_SSO_PROVIDER_SECRET_VERSION=v1
+# SECRET_SSO_PROVIDER_SECRET_VERSION=v1