website/sponsors.html: add IPComm as a silver sponsor

IPCOMM GmbH is a German company that develop industrial gateways and
inter-network communication solutions.

They agreed to sponsor the LTS maintenance for 2026. We thanks them for
their contribution.

 - https://www.ipcomm.de/
 - https://www.ipcomm.de/article/AboutUs/en/sheet.html

For more informations about the LTS sponsorship, see:

 - https://buildroot.org/lts.html

Signed-off-by: Thomas Perale <thomas.perale@mind.be>
Signed-off-by: Julien Olivain <ju.o@free.fr>

docs/website/sponsors.html

@@ -51,6 +51,26 @@
     </div>
     </div>
 
+    <div class="panel-body">
+      <h3>Silver Sponsors</h3>
+      <div class="sponsors-container">
+        <div class="sponsor-entry">
+          <div class="panel panel-default panel-lts-sponsor">
+            <div class="panel-body">
+              <div class="sponsor-title">
+                <a href="https://www.ipcomm.de">
+                  <img class="img-responsive center-block" style="height: 100%;" src="images/ipcomm-logo.png"/>
+                </a>
+              </div>
+              <div class="sponsor-body">
+                <a href="https://www.ipcomm.de">IPComm</a>
+              </div>
+            </div>
+          </div>
+        </div>
+      </div>
+    </div>
+
     <div class="panel panel-primary">
     <div class="panel-heading">Current sponsors</div>
     <div class="panel-body">