Update build instructions in devnotes.html

Making the instructions more specific, so the developer does not need to figure it out through trial and error.

This will resolve this issue: #845

Author: ScottHutchinson

docs/devnotes.html

@@ -76,7 +76,7 @@ <h2><a name="Building-and-NuGet" class="anchor" href="#Building-and-NuGet">Build
 <td class="snippet"><pre class="fssnip"><code lang="text">git clone https://github.com/fsharp/FSharp.Compiler.Service
 cd FSharp.Compiler.Service
 </code></pre></td></tr></table>
-<p>Now follow build everything by running <code>build.cmd</code> (Windows) or <code>build.sh</code> (Linux + Mac OS).
+<p>Now follow build everything by running <code>.\fcs\build.cmd</code> (Windows) or <code>./fcs/build.sh</code> (Linux + Mac OS).
 The output will be located in the <code>bin</code> directory. If you also wish to build the documentation
 and NuGet package, run <code>build Release</code> (this also attempts to publish the documentation to
 GitHub, which only works if you have access to the GitHub repository).</p>