add link to github repo

index.html

@@ -68,7 +68,8 @@
                     target="_blank" href="example_encrypted.html">example</a>).
             </p>
             <p>
-                The tool is also available as <a href="https://npmjs.com/package/staticrypt">a CLI on NPM</a>.
+                The tool is also available as <a href="https://npmjs.com/package/staticrypt">a CLI on NPM</a> and is <a
+                    href="https://github.com/robinmoisson/staticrypt">open source on GitHub</a>.
             </p>
             <br>