Implement config files

docs/usage.md

@@ -6,7 +6,7 @@ The linter is installed as a Django app and is integrated through the Django man
 
 `python manage.py lintmigrations [GIT_COMMIT_ID] ...`
 
-Detailed command line options:
+Below the detailed command line options, which can all also be defined using a config file (`setup.cfg`, `tox.ini`, `myproject.toml`, `.editorconfig`, `.django_migration_linter.cfg`):
 
 |                   Parameter                                  |                                        Description                                                                          |
 |--------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------|
@@ -27,6 +27,16 @@ Detailed command line options:
 |`--quiet or -q {ok,ignore,warning,error}`                     | Suppress certain output messages, instead of writing them to stdout.                                                        |
 |`--warnings-as-errors`                                        | Handle warnings as errors and therefore return an error status code if we should.                                           |
 
+## File configuration
+
+Example `setup.cfg` file:
+
+```
+[django_migration_linter]
+no_cache = True
+exclude_apps = users
+```
+
 ## Ignoring migrations
 
 You can also ignore migrations by adding an `IgnoreMigration()` to your migration operations: