docs: ignore local data folders, document production bind mounts

.gitignore

@@ -58,4 +58,9 @@ Thumbs.db
 *.swo
 
 # Docker
-docker-compose.override.yml
+docker-compose.override.yml
+
+# Local data folders (bind mounts used in production instead of named volumes)
+db_data/
+wordpress_data/
+redis_data/