[Doc] Add link to contact MArmelab experts

Author: fzaninotto

docs/documentation.html

@@ -214,6 +214,18 @@ <h2>Recipes</h2>
                     </div>
                 </div>
             </div>
+            <div
+                class="container"
+                style="text-align: center; padding-top: 0; color: #888"
+            >
+                Need help with your React-admin app?
+                <br />
+                Turn to Marmelab, its creators and seasoned full-stack JS
+                development agency.
+                <br />
+                <a href="mailto:react-admin-ee@marmelab.com">Get in touch</a>
+                to hire an expert for a day, or a team for a month.
+            </div>
         </main>
 
         <script src="js/materialize.min.js"></script>