Highlight rustfmt config doc version

Author: Herrtian

docs/index.html

@@ -58,10 +58,22 @@
         .searchCondition {
           display: flex;
           flex-wrap: wrap;
+          position: sticky;
+          top: 0;
+          z-index: 1;
+          padding: 12px 0;
+          background: #fff;
+          border-bottom: 1px solid #d1d5da;
         }
         .searchCondition > div {
           margin-right: 30px;
         }
+        .version-note {
+          flex-basis: 100%;
+          margin-top: 8px;
+          color: #57606a;
+          font-size: 0.9em;
+        }
         .header-link {
           position: relative;
         }
@@ -100,6 +112,9 @@
                     </option>
                   </select>
               </div>
+              <div class="version-note">
+                Configuration options can change between rustfmt versions. Select the version that matches the rustfmt you use.
+              </div>
             </div>
             <div v-html="aboutHtml"></div>
             <div v-html="configurationAboutHtml"></div>