document serviceWorker register option (#3395)

* document serviceWorker register option

* Update documentation/docs/14-configuration.md

Co-authored-by: Rich Harris <[email protected]>

Author: ignatiusmb

documentation/docs/14-configuration.md

@@ -232,6 +232,7 @@ Enables or disables the client-side [router](#page-options-router) app-wide.
 
 An object containing zero or more of the following values:
 
+- `register` - if set to `false`, will disable automatic service worker registration
 - `files` - a function with the type of `(filepath: string) => boolean`. When `true`, the given file will be available in `$service-worker.files`, otherwise it will be excluded.
 
 ### target