use dedicated bootstrap class

Co-authored-by: Katja Süss <[email protected]>

Author: MAX-786

docs/_templates/search-field.html

@@ -2,7 +2,7 @@
   <div class="input-group">
     <label for="q" class="sr-only">Search string
     </label>
-    <div class="input-group-prepend">
+    <div class="input-group-append">
       <span class="input-group-text" id="shortcut">
         <kbd id="search-shortcut">⌘</kbd>&nbsp;<kbd>K</kbd>
       </span>