apps: Add comments to app service AppType enum

No code change, just comments.

Bug: none
Change-Id: I16fe794ae2e153c0bba3073372d8afacd01f5cd7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2394375
Auto-Submit: James Cook <jamescook@chromium.org>
Commit-Queue: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804638}

components/services/app_service/public/mojom/types.mojom

@@ -93,10 +93,10 @@ enum AppType {
   kExtension,  // Extension-backed app.
   kWeb,        // Web app.
   kMacNative,  // Native Mac app.
-  kPluginVm,   // Plugin VM app.
-  kLacros,     // Lacros app.
+  kPluginVm,   // Plugin VM app, see go/pluginvm.
+  kLacros,     // Lacros browser app, see //docs/lacros.md.
   kRemote,     // Remote app.
-  kBorealis,   // Borealis app.
+  kBorealis,   // Borealis app, see go/borealis-app.
 };
 
 // Whether an app is ready to launch, i.e. installed.