changelog-web: Added read more link

Added a Read more link under the color legend for the changelog feature. This link redirects to the readme page.

BUG=b/160901711
TEST=run local

Change-Id: I305ebb171d696d7781f90da095fd6205677faeb7
diff --git a/src/cmd/changelog-webapp/static/css/changelog.css b/src/cmd/changelog-webapp/static/css/changelog.css
index 8a51e20..3140f47 100644
--- a/src/cmd/changelog-webapp/static/css/changelog.css
+++ b/src/cmd/changelog-webapp/static/css/changelog.css
@@ -48,6 +48,11 @@
     margin: 3px 0px 3px 4px;
 }
 
+.sha-legend a {
+    font-size: 14px;
+    margin: 4px;
+}
+
 .circle {
     border-radius: 50%;
     display: inline-block;
diff --git a/src/cmd/changelog-webapp/static/templates/changelog.html b/src/cmd/changelog-webapp/static/templates/changelog.html
index 877d4cf..d5c103f 100644
--- a/src/cmd/changelog-webapp/static/templates/changelog.html
+++ b/src/cmd/changelog-webapp/static/templates/changelog.html
@@ -81,6 +81,7 @@
             Commits present in <b>{{.Source}}</b> but not in <b>{{.Target}}</b>
           </span>
         </div>
+        <a href="/readme/">Read more</a>
       </div>
     {{end}}
     {{range $table := .RepoTables}}