plugin.ts: Describe private counterpart functions

Addresses Will's comments.

src/node/routes/apps.ts

@@ -1,6 +1,9 @@
 import * as express from "express"
 import { PluginAPI } from "../plugin"
 
+/**
+ * Implements the /api/applications endpoint
+ */
 export function router(papi: PluginAPI): express.Router {
   const router = express.Router()