replace command-like link to repo by a "clone me" button in the Sourc…

…e code section of Download index page (#285)

themes/grass/layouts/download/list.html

@@ -41,8 +41,8 @@ <h2 class="section-title">Download your free and open source copy</h2>
                   <div class="col-4 text-center"><object type="image/svg+xml" data="{{.Site.BaseURL}}/images/logos/grasslogo.svg" class="grasslogo"></object></div>
                   <div class="col-8">
 		    <h3 class="mt-20">GRASS GIS source code</h3>
-		    <p>The GRASS GIS source code is available on <a href="https://github.com/OSGeo/grass" target="_blank"><i class="fa fa-github"></i> Github</a>, see all <a href="https://github.com/OSGeo/grass/tags">source code archives</a> for releases (zip and tarball files). Alternatively, find the latest tarballs and snapshots at <a href="https://grass.osgeo.org/grass80/source/">https://grass.osgeo.org/grass80/source/</a>. Or, clone the repo:</p>
-		    <p class="command d-none d-lg-block"><a href="https://github.com/OSGeo/grass"> $ git clone https://github.com/OSGeo/grass </a></p>
+		    <p>The GRASS GIS source code is available on <a href="https://github.com/OSGeo/grass" target="_blank"><i class="fa fa-github"></i> Github</a>, see all <a href="https://github.com/OSGeo/grass/tags">source code archives</a> for releases (zip and tarball files). Alternatively, find the latest tarballs and snapshots at <a href="https://grass.osgeo.org/grass80/source/">https://grass.osgeo.org/grass80/source/</a>.</p>
+            <a class="btn btn-primary" href="https://github.com/OSGeo/grass" target="_blank">Clone me at <i class="fa fa-github"></i></a>
                   </div>
                 </div>
               </div>