doc: update instructions on home page

Document how to run the example on the home page in more detail.

Apparently our Windows brethren are prone to double-clicking on the
binary instead of running it from the command line.

Fixes #4854.

doc/index.html

@@ -89,7 +89,9 @@ <h2>An example: Webserver</h2>
 }).listen(1337, '127.0.0.1');
 console.log('Server running at http://127.0.0.1:1337/');</pre>
 
-              <p>To run the server, put the code into a file <code>example.js</code> and execute it with the <code>node</code> program:</p>
+              <p>To run the server, put the code into a file
+              <code>example.js</code> and execute it with the
+              <code>node</code> program from the command line:</p>
               <pre class="sh_none">
 % node example.js
 Server running at http://127.0.0.1:1337/</pre>