Add missing properties in option typedef

src/ol/source/ImageMapGuide.js

@@ -13,6 +13,10 @@ import {appendParams} from '../uri.js';
 /**
  * @typedef {Object} Options
  * @property {string} [url] The mapagent url.
+ * @property {null|string} [crossOrigin] The `crossOrigin` attribute for loaded images.  Note that
+ * you must provide a `crossOrigin` value if you are using the WebGL renderer or if you want to
+ * access pixel data with the Canvas renderer.  See
+ * {@link https://developer.mozilla.org/en-US/docs/Web/HTML/CORS_enabled_image} for more detail.
  * @property {number} [displayDpi=96] The display resolution.
  * @property {number} [metersPerUnit=1] The meters-per-unit value.
  * @property {boolean} [hidpi=true] Use the `ol/Map#pixelRatio` value when requesting