diff --git a/src/ohmyapi/core/runtime.py b/src/ohmyapi/core/runtime.py
index fdb811a..6778024 100644
--- a/src/ohmyapi/core/runtime.py
+++ b/src/ohmyapi/core/runtime.py
@@ -121,6 +121,12 @@ class Project:
     def build_aerich_command(
         self, app_label: str, db_url: Optional[str] = None
     ) -> AerichCommand:
+        """
+        Build Aerich command for app with given app_label.
+
+        Aerich needs to see only the app of interest, but with the extra model
+        "aerich.models".
+        """
         if app_label not in self._apps:
             raise RuntimeError(f"App '{app_label}' is not registered")