Add API docs for `loopback.static`.

docs.json

@@ -12,6 +12,7 @@
     "lib/middleware/status.js",
     "lib/middleware/token.js",
     "lib/middleware/urlNotFound.js",
+    "lib/middleware/static.js",
 { "title": "Built-in models", "depth": 2 },
     "common/models/access-token.js",
     "common/models/acl.js",

lib/middleware/static.js

@@ -0,0 +1,11 @@
+/**
+ * Serve static assets of a LoopBack application.
+ *
+ * @param {string} root The root directory from which the static assets are to
+ * be served.
+ * @param {object} options Refer to
+ *   [express documentation](http://expressjs.com/4x/api.html#express.static)
+ *   for the full list of available options.
+ * @header loopback.static(root, [options])
+ */
+module.exports = require('express').static;