Marked width/height as readonly and added docs. Fix phaserjs#4806

Author: photonstorm

src/physics/arcade/Body.js

@@ -190,7 +190,7 @@ var Body = new Class({
         this.rotation = gameObject.angle;
 
         /**
-         * The Body's rotation, in degrees, during the previous step.
+         * The Body rotation, in degrees, during the previous step.
          *
          * @name Phaser.Physics.Arcade.Body#preRotation
          * @type {number}
@@ -199,22 +199,26 @@ var Body = new Class({
         this.preRotation = gameObject.angle;
 
         /**
-         * The width of the Body's boundary, in pixels.
-         * If the Body is circular, this is also the Body's diameter.
+         * The width of the Body boundary, in pixels.
+         * If the Body is circular, this is also the diameter.
+         * If you wish to change the width use the `Body.setSize` method.
          *
          * @name Phaser.Physics.Arcade.Body#width
          * @type {number}
+         * @readonly
          * @default 64
          * @since 3.0.0
          */
         this.width = width;
 
         /**
-         * The height of the Body's boundary, in pixels.
-         * If the Body is circular, this is also the Body's diameter.
+         * The height of the Body boundary, in pixels.
+         * If the Body is circular, this is also the diameter.
+         * If you wish to change the height use the `Body.setSize` method.
          *
          * @name Phaser.Physics.Arcade.Body#height
          * @type {number}
+         * @readonly
          * @default 64
          * @since 3.0.0
          */