Update index.html

Added the git repository url

index.html

@@ -256,6 +256,7 @@
                          ' - windows are dragable\n' +
                          ' - in each window, there is a file context menu\n' +
                          ' - have fun typing\n' +
+                         'https://git.rintyuu.dev/rintyuu/notepad\n\n' +
                          'contact me at me@rintyuu.uk for suggestions';
 
         helpWindow.appendChild(titleBar);