add masto-fe docs

docs/docs/configuration/cheatsheet.md

@@ -283,14 +283,19 @@ config :pleroma, :frontends,
     "name" => "swagger-ui",
     "ref" => "stable",
     "enabled" => true
+  },
+  mastodon: %{
+    "name" => "mastodon-fe",
+    "ref" => "akkoma"
   }
 ```
 
 * `:primary` - The frontend that will be served at `/`
 * `:admin` - The frontend that will be served at `/pleroma/admin`
 * `:swagger` - Config for developers to act as an API reference to be served at `/akkoma/swaggerui/` (trailing slash _needed_). Disabled by default.
+* `:mastodon` - The mastodon-fe configuration. This shouldn't need to be changed. This is served at `/web` when installed.
 
-### :static_fe
+### :static\_fe
 
 Render profiles and posts using server-generated HTML that is viewable without using JavaScript.