Added documentation footer

The documentation will be licensed under CC BY 3.0, instead of
under the MIT license like the rest of the code.

docs/_includes/footer.html

@@ -0,0 +1,11 @@
+<footer>
+  Select2 is licensed under the
+  <a href="https://github.com/ivaynberg/select2/blob/master/LICENSE.md">
+    MIT license.
+  </a>
+  The documentation is licensed under
+  <a href="https://creativecommons.org/licenses/by/3.0/">CC BY 3.0.</a>
+  Maintained by
+  <a href="https://github.com/kevin-brown">Kevin Brown</a> and
+  <a href="https://github.com/ivaynberg">Igor Vaynberg</a>.
+</footer>

docs/_includes/head.html

@@ -18,4 +18,5 @@
 
 <style type="text/css">
   .navbar-inverse .navbar-brand { color: #fff; }
+  footer { background-color: #eee; margin-top: 1em; padding: 1em; text-align: center; }
 </style>