docs(erasing): Update README (fabricjs#7170)

Author: ShaMan123

README.md

@@ -201,6 +201,7 @@ These are the optional modules that could be specified for inclusion, when build
 - **easing** — Adds support for animation easing functions
 - **node** — Adds support for running fabric under node.js, with help of [jsdom](https://github.com/tmpvar/jsdom) and [node-canvas](https://github.com/learnboost/node-canvas) libraries.
 - **freedrawing** — Adds support for free drawing
+- **erasing** — Adds support for object erasing using an eraser brush
 - **gestures** — Adds support for multitouch gestures with help of [Event.js](https://github.com/mudcube/Event.js)
 - **object_straightening** — Adds support for rotating an object to one of 0, 90, 180, 270, etc. depending on which is angle is closer.
 - **animation** — Adds support for animation (`fabric.util.animate`, `fabric.util.requestAnimFrame`, `fabric.Object#animate`, `fabric.Canvas#fxCenterObjectH/#fxCenterObjectV/#fxRemove`)
@@ -250,6 +251,7 @@ For example:
 
 - [Fabric on Bountysource](https://www.bountysource.com/trackers/23217-fabric-js)
 - [Fabric on CodeTriage](http://www.codetriage.com/kangax/fabric.js)
+- [Contributing](./CONTRIBUTING.md)
 
 ### Staying in touch