add master doc warning

Author: fantix

docs/theme/layout.html

@@ -125,6 +125,16 @@
                     {% if pagename != master_doc and toc.count('href') > 1 %}
                         <hr>
                     {% endif %}
+                    {% if "master" in VERSION %}
+                        <div class="version-warning">
+                            {% if language.startswith('zh') %}
+                                您正在浏览 master 分支，该文档可能涉及尚未发布的功能。
+                            {% else %}
+                                You're on the master branch. This documentation may include
+                                functionality that is not released yet.
+                            {% endif %}
+                        </div>
+                    {% endif %}
                 </div>
                 <div class="add-your-lang">
                     <a href="https://www.transifex.com/decentfox-studio/gino_1_0/"

docs/theme/static/css/gino.css

@@ -394,6 +394,12 @@ div.search i {
     color: var(--v-info-light);
 }
 
+.version-warning {
+    border: 1px solid #757575;
+    background-color: #ffaaaa;
+    padding: 8px;
+}
+
 h1 {
     font-size: 32px;
     margin: 32px 0 20px 0;