Update enterprise_sidebar.html

Adding MIT license to sidebar

Author: nrios14

_includes/enterprise_sidebar.html

@@ -83,6 +83,7 @@ <h3>Travis CI Docs</h3>
   <section class="sidebar-notice">
     <p>This documentation site is open source.
       The <a href="https://github.com/travis-ci/docs-travis-ci-com">README in our Git repository</a> explains how to contribute.</p>
+    <p>Travis CI relies on Open Source <a href="/user/open_source_licence/">licensing information</a>.</p>
   </section>
 
 </div><!-- /#sidebar -->