frontend: add link to github repo from footer

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

src/frontend/templates/footer.html

@@ -1,7 +1,12 @@
 {{ define "footer" }}
     <footer class="py-5 px-5">
         <div class="container">
-            <p>&copy; 2018 Google Inc</p>
+            <p>
+                &copy; 2018 Google Inc
+                <span class="text-muted">
+                    <a href="https://github.com/GoogleCloudPlatform/microservices-demo/">(Source Code)</a>
+                </span>
+            </p>
             <p>
                 <small class="text-muted">
                     This website is hosted for demo purposes only. It is not an
@@ -12,7 +17,6 @@
                 {{ if $.session_id }}session-id: {{ $.session_id }}</br>{{end}}
                 {{ if $.request_id }}request-id: {{ $.request_id }}</br>{{end}}
             </small>
-            
         </div>
     </footer>
     <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js" integrity="sha384-smHYKdLADwkXOn1EmN1qk/HfnUcbVRZyYmZ4qpPea6sjB/pTJ0euyQp0Mk8ck+5T" crossorigin="anonymous"></script>