README.md in rubocop-oracle-0.1.0 vs README.md in rubocop-oracle-0.2.0

@@ -17,9 +17,37 @@
 
 ```ruby
 gem 'rubocop-oracle'
 ```
 
+## Cops
+
+This gem contains `Oracle/OnlineIndex` cop to check if indexing is possible without stopping Rails application' service using Oracle.
+The cop supports safe migration for your production environment.
+
+### `Oracle/OnlineIndex` cop
+
+This cop checks for uses `options: online` option on `add_index`.
+The `ONLINE` option is required if you want to run with OLTP when indexing migration in Oracle.
+
+```ruby
+# bad
+add_index :table_name, :column_name
+
+# good
+add_index :table_name, :column_name, options: :online
+```
+
+By specifying `MigratedSchemaVersion` option, migration files that have been migrated can be ignored.
+
+```yaml
+# .rubocop.yml
+Oracle/OnlineIndex:
+  MigratedSchemaVersion: '202104130150' # Migration files lower than or equal to '202104130150' will be ignored.
+```
+
+This prevents detection of migration files that have already been applied to the production environment.
+
 ## Usage
 
 You need to tell RuboCop to load the Oracle extension. There are three
 ways to do this: