docs(DEVELOPER) Add documentation for CordovaFunctionOverride decorat…

…or (danielsogl#2029)

DEVELOPER.md

@@ -209,4 +209,13 @@ Example:
 someMethod(): Promise<any> {
   // anything here will only run if the plugin is available
 }
+```
+
+#### CordovaFunctionOverride
+Wrap a stub function in a call to a Cordova plugin, checking if both Cordova and the required plugin are installed.
+
+Example:
+```ts
+@CordovaFunctionOverride()
+someMethod(): Observable<any> { return; }
 ```