Add docs for fresco plugin

Summary:
Now that we finally have something we can screenshot ...

Just for the features page right now, will add some
"installation" instructions next.

Reviewed By: oprisnik

Differential Revision: D15898050

fbshipit-source-id: 9dfd3b1121799e7069336aac845ba2abdb3e42df

docs/features/images-plugin.md

@@ -0,0 +1,30 @@
+---
+id: images-plugin
+title: Images
+---
+
+The images plugin allows you to inspect what images were fetched, where they are
+coming from and selectively clear caches. Currently, the plugin supports
+[Fresco](https://github.com/facebook/fresco/) as backend.
+
+![Images plugin](/docs/assets/images-plugin.png)
+
+## Cache Inspector
+
+Images are grouped by the different caching layers they are stored in. The current
+fill rate of the cache is shown and you can choose to selectively clear caches.
+
+
+## Attribution
+
+Images can be annotated with attributes that can help to determine the context in
+which an image was loaded and displayed. You can use that information to filter
+by a particular surface or only inspect images that are in the critical path
+of your application, for instance during cold start.
+
+## Leak Tracking
+
+Dealing with large resources can require special APIs to be used that circumvent
+usual garbage collection. The plugin allows to track `CloseableReference`s for
+Fresco on Android that weren't properly closed, which can help you improve
+the performance of your app.

website/i18n/en.json

@@ -66,6 +66,9 @@
       "features/databases-plugin": {
         "title": "Databases"
       },
+      "features/images-plugin": {
+        "title": "Images"
+      },
       "features/index": {
         "title": "Features"
       },

website/sidebars.json

@@ -6,6 +6,7 @@
       "features/layout-plugin",
       "features/network-plugin",
       "features/databases-plugin",
+      "features/images-plugin",
       "features/sandbox-plugin",
       "features/shared-preferences-plugin",
       "features/leak-canary-plugin",