Add documentation for deploying without Redis as a dependency (#304)

Author: j-lea

deployment/README.md

@@ -201,11 +201,14 @@ You can customise this window with the `SESSION_TIME` env variable to the `env`
 SESSION_TIME=60 ./deploy <app-name>
 ```
 
+### [From 4.3.0] Removing Redis dependency
+If you are on a later version than 4.3.0 and using Postgres, Redis is no longer required. Instead set the environment variable `USE_POSTGRES_FOR_ACTION_CABLE=true` on deploy.
+
 ## Testing your deployment
 
 1. Log in to the Postfacto admin dashboard
 1. Create a new admin user for the test to use by clicking on 'Admin Users' and then 'New Admin User'. Take note of the email and password you use, as these will be used in the next step
 1. Run the smoke test script from the root of the package directory:
     ```bash
     ./smoke-test.sh <app-url> <app-admin-url> <test-admin-email> <test-admin-password>
-    ```
+    ```