Merge pull request twbs#10797 from twbs/input-groups-xref

add cross-reference to Input Groups in CSS Form docs; fixes twbs#10792

css.html

@@ -1661,6 +1661,10 @@ <h4>Type declaration required</h4>
 {% highlight html %}
 <input type="text" class="form-control" placeholder="Text input">
 {% endhighlight %}
+    <div class="bs-callout bs-callout-info">
+      <h4>Input groups</h4>
+      <p>To add integrated text or buttons before and/or after any text-based <code>&lt;input&gt;</code>, <a href="../components/#input-groups">check out the input group component.</a></p>
+    </div>
 
     <h3>Textarea</h3>
     <p>Form control which supports multiple lines of text. Change <code>rows</code> attribute as necessary.</p>