Add bottom links for sign-in page so I can get to Public area

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/generic/common.scss

@@ -337,3 +337,7 @@ table {
 .wiki .highlight, .note-body .highlight {
   margin-bottom: 9px;
 }
+
+.footer-links a {
+  margin-right: 15px;
+}

app/views/layouts/devise.html.haml

@@ -18,3 +18,9 @@
               = brand_text
           .col-md-5
             = yield
+    %hr
+    .container
+      .footer-links
+        = link_to "Explore public projects", public_projects_path
+        = link_to "Documentation", "http://doc.gitlab.com/"
+        = link_to "About GitLab", "https://about.gitlab.com/"