Add Rotate Mode to mode docs (#759)

Author: tempranova

docs/MODES.md

@@ -68,6 +68,7 @@ _please feel free to add your own modes to this list via a PR_
 -   [Static Mode](https://github.com/mapbox/mapbox-gl-draw-static-mode): Turn off interactions
 -   [Cut/Split Line Mode](https://github.com/BrunoSalerno/mapbox-gl-draw-cut-line-mode): Cut/split lineStrings functionality
 -   [Freehand Mode](https://github.com/bemky/mapbox-gl-draw-freehand-mode): Add Freehand functionality to draw polygon mode
+-   [Rotate Mode](https://github.com/mapstertech/mapbox-gl-draw-rotate-mode): Add ability to Rotate GL Draw features
 
 ## Life Cycle Functions