docs(1815): add trademarks link ref to linux foundation

Signed-off-by: Martin Jirku <martin@jirku.sk>

docs/_includes/footer.html

@@ -7,6 +7,14 @@
       Apache License 2.0 licensed project
       <br>
       © {{ site.year }} Kompose Authors -- All Rights Reserved
+      <br />
+      <a
+        class="trademarks"
+        href="https://www.linuxfoundation.org/legal/trademark-usage"
+        target="_blank"
+        ref="noopener"
+        >Trademarks</a
+      >
     </span>
   </div>
   <div class="container">