fix(docs): clean up npm start docs

Adds an example, and a note about how this differs than node's default
behavior

PR-URL: #2459
Credit: @wraithgar
Close: #2459
Reviewed-by: @darcyclarke

docs/content/commands/npm-start.md

@@ -12,13 +12,39 @@ npm start [-- <args>]
 
 ### Description
 
-This runs an arbitrary command specified in the package's `"start"` property of
-its `"scripts"` object. If no `"start"` property is specified on the
-`"scripts"` object, it will run `node server.js`.
+This runs a predefined command specified in the `"start"` property of
+a package's `"scripts"` object.
+
+If the `"scripts"` object does not define a  `"start"` property, npm
+will run `node server.js`.
+
+Note that this is different from the default node behavior of running
+the file specified in a package's `"main"` attribute when evoking with
+`node .`
 
 As of [`npm@2.0.0`](https://blog.npmjs.org/post/98131109725/npm-2-0-0), you can
 use custom arguments when executing scripts. Refer to [`npm run-script`](/commands/npm-run-script) for more details.
 
+### Example
+
+```json
+{
+  "scripts": {
+    "start": "node foo.js"
+  }
+}
+```
+
+```bash
+npm start
+
+> npm@x.x.x start
+> node foo.js
+
+(foo.js output would be here)
+
+```
+
 ### See Also
 
 * [npm run-script](/commands/npm-run-script)