fix: Add usage

Author: Stephan Wentz

README.md

@@ -8,3 +8,13 @@ Register the commands in your `services.yaml`.
 
     Brainbits\DatabaseCommand\Command\WaitForDatabaseCommand: ~
 ```
+
+# Usage
+
+```sh
+$ bin/console brainbits:database:wait-for-database --retry-seconds 3 --retry-count 100
+```
+
+```sh
+$ bin/console brainbits:database:schema-exists
+```