Add missing sidebar template.

Author: lohedges

doc/source/_templates/sidebar/search.html

@@ -0,0 +1,12 @@
+<form class="sidebar-search-container" method="get" action="{{ pathto('search') }}" role="search">
+  <input class="sidebar-search" placeholder="{{ _("Search") }}" name="q" aria-label="{{ _("Search" ) }}">
+  <input type="hidden" name="check_keywords" value="yes">
+  <input type="hidden" name="area" value="default">
+</form>
+<div id="searchbox"></div>
+<div class="sidebar-search">
+  <div class="version_container">
+    <div class="version_label">Branch</div>
+    <div id="version_box" class="version_box"></div>
+  </div>
+</div>