Erd generating doc improvement (#37808)

* docs(airflow): fix outdated er digagram generating script path

* docs(scripts): improve run_migration_reference script message

(cherry picked from commit 46c5713)

docs/apache-airflow/database-erd-ref.rst

@@ -33,6 +33,6 @@ Here is the current Database schema diagram.
    `db command <cli-and-env-variables-ref.html#db>`_ for the commands that you can use to manage
    the migrations.
 
-.. This image is automatically generated by pre-commit via ``scripts/ci/pre_commit/pre_commit_update_diagram.py``
+.. This image is automatically generated by pre-commit via ``scripts/ci/pre_commit/pre_commit_update_er_diagram.py``
 
 .. image:: img/airflow_erd.svg

scripts/in_container/run_migration_reference.py

@@ -174,9 +174,9 @@ def ensure_filenames_are_sorted(revisions):
             "alembic merge -m 'merge heads " + ", ".join(head_prefixes) + "' " + " ".join(unmerged_heads)
         )
         raise SystemExit(
-            "You have multiple alembic heads; please merge them with the `alembic merge` command "
-            f"and re-run pre-commit. It should fail once more before succeeding. "
-            f"\nhint: `{alembic_command}`"
+            "You have multiple alembic heads; please merge them with by running `alembic merge` command under "
+            f'"airflow" directory (where alembic.ini located) and re-run pre-commit. '
+            f"It should fail once more before succeeding.\nhint: `{alembic_command}`"
         )
     for old, new in renames:
         os.rename(old, new)