docs(deployment): add note about Refresh Workers keeping refreshKey up-to-date

Author: hassankhan

docs/content/Deployment/Overview.mdx

@@ -150,11 +150,13 @@ has access to the data schema files.
 
 ## Refresh Worker
 
-Refresh Worker updates the pre-aggregations and in-memory cache in the
-background.
+A Refresh Worker updates pre-aggregations and the in-memory cache in the
+background. They also keep the refresh keys up-to-date for all defined schemas
+and pre-aggregations.
 
-[Cube.js Docker image][dh-cubejs] is used for Refresh Worker too. To make
-service act as a Refresh Worker `CUBEJS_REFRESH_WORKER=true` should be set.
+[Cube.js Docker image][dh-cubejs] can be used for creating Refresh Workers; to
+make the service act as a Refresh Worker, `CUBEJS_REFRESH_WORKER=true` should be
+set in the environment variables.
 
 ## Cube Store