chore(docs): Add note about icon_options (#28363)

Author: LekoArts

packages/gatsby-plugin-manifest/README.md

@@ -202,7 +202,8 @@ module.exports = {
         display: `standalone`,
         icon: `src/images/icon.png`,
         icon_options: {
-          // For all the options available, please see the additional resources below.
+          // For all the options available,
+          // please see the section "Additional Resources" below.
           purpose: `any maskable`,
         },
       },
@@ -444,7 +445,7 @@ Internet Explorer is the only other major browser that doesn't support the web a
 This article from the Chrome DevRel team is a good intro to the web app
 manifest — https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/
 
-For more information, see the [W3C specification](https://www.w3.org/TR/appmanifest/), [Mozilla documentation](https://developer.mozilla.org/en-US/docs/Web/Manifest) or [Web.Dev guide](https://web.dev/add-manifest/).
+For more information, see the [W3C specification](https://www.w3.org/TR/appmanifest/), [Mozilla documentation](https://developer.mozilla.org/en-US/docs/Web/Manifest) or [Web.Dev guide](https://web.dev/add-manifest/). More information about `icon_options` can be found in [this Web.Dev guide](https://web.dev/maskable-icon/).
 
 ### Plugin options validation