Add a comment with all features enabled by default

In order to uncomment it in the Makefile of GDK

config.yml.example

@@ -53,9 +53,7 @@ audit_usernames: false
 # Migration to Go: anything listed here has two implementations. Use these flags
 # to try the new implementations out, or to revert to the old behaviour if there
 # problems arise.
-migration:
-  enabled: false
-  features: []
+# migration: { enabled: true, features: ['discover', '2fa_recovery_codes', 'git-receive-pack', 'git-upload-pack', 'git-upload-archive', 'git-lfs-authenticate'] }
 
 # Distributed Tracing. GitLab-Shell has distributed tracing instrumentation.
 # For more details, visit https://docs.gitlab.com/ee/development/distributed_tracing.html