chore: add new sponsor to docs page

Author: jcbrand

docs/source/_templates/sponsors.html

@@ -10,6 +10,10 @@ <h4 class="sidebar-title">Sponsored by</h4>
             <img style="width: 9em" src="https://conversejs.org/logo/blokt.png" alt="Blokt Crypto & Privacy">
         </a>
     </li>
+    <li><a href="https://www.litslink.com/?utm_source=conversejs" target="_blank" rel="noopener">
+            <img style="height: 2.5em" src="https://conversejs.org/media/logos/litslink-light.svg" alt="LITSLINK software development">
+        </a>
+    </li>
     <li><a href="https://www.keycdn.com/?utm_source=conversejs" target="_blank" rel="noopener">
             <img style="height: 2.5em" src="https://conversejs.org/logo/keycdn.png" alt="KeyCDN">
         </a>