docs: add cmd/github cache to readme

README.md

@@ -90,7 +90,7 @@ You can also use the `--watched` option to mark all Aired Unwatched Episodes of
 
 ## GitHub
 
-`cmd/github` fetches Repositories and Recent Contributions for a specific [GitHub](https://github.com/) User.
+`cmd/github` fetches Repositories and Recent Contributions for a specific [GitHub](https://github.com/) User. Repositories are cached if the `alfred_workflow_cache` environment variable (automatically provided by Alfred) is set.
 
 ### Usage
 
@@ -115,6 +115,8 @@ $ github
 }
 ```
 
+You can use the `--clear` option to clear the cached GitHub Repositories.
+
 ### Configuration
 
 `cmd/github` consumes an environment variables that should be [provided by Alfred](https://www.alfredapp.com/help/workflows/advanced/variables/#environment) when invoking the script in a workflow: