update fastlane docs

Author: bbriatte

fastlane/README.md

@@ -561,4 +561,4 @@ import_from_git(
 
 This README.md is auto-generated and will be re-generated every time [fastlane](https://fastlane.tools) is run.
 More information about fastlane can be found on [https://fastlane.tools](https://fastlane.tools).
-The documentation of fastlane can be found on [GitHub](https://github.com/fastlane/fastlane/tree/master/fastlane).
+The documentation of fastlane can be found on [https://docs.fastlane.tools](https://docs.fastlane.tools).