Updated fixedToCamera docs to reflect non-nesting (phaserjs#1596)

Author: photonstorm

src/core/Group.js

@@ -174,6 +174,7 @@ Phaser.Group = function (game, parent, name, addToStage, enableBody, physicsBody
 
     /**
     * If this object is {@link #fixedToCamera} then this stores the x/y position offset relative to the top-left of the camera view.
+    * If the parent of this Group is also `fixedToCamera` then the offset here is in addition to that and should typically be disabled.
     * @property {Phaser.Point} cameraOffset
     */
     this.cameraOffset = new Phaser.Point();

src/gameobjects/components/FixedToCamera.js

@@ -16,6 +16,7 @@ Phaser.Component.FixedToCamera.prototype = {
     * A Sprite that is fixed to the camera uses its x/y coordinates as offsets from the top left of the camera. These are stored in Sprite.cameraOffset.
     * Note that the cameraOffset values are in addition to any parent in the display list.
     * So if this Sprite was in a Group that has x: 200, then this will be added to the cameraOffset.x
+    * Be careful not to set `fixedToCamera` on Game Objects which are in Groups that already have fixedToCamera enabled on them.
     * @property {boolean} fixedToCamera
     */
     fixedToCamera: false,