docs/website/sponsors.html: mention LTS sponsors

Since the LTS sponsoring program hasn't started yet (it will hopefully
start in September), this is just placeholder text. The first paragraph
will stay however.

Signed-off-by: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Romain Naour <romain.naour@smile.fr>

docs/website/sponsors.html

@@ -4,6 +4,17 @@
 <div class="row nh"><!-- current sponsor row -->
 <div class="col-lg-10 col-lg-offset-1 col-md-12 col-sm-12 col-xs-12">
 
+    <div class="panel panel-primary">
+    <div class="panel-heading">LTS sponsors</div>
+    <div class="panel-body">
+      <p>The maintenance of the Long Term Support branch of Buildroot is
+         possible thanks to the sponsors of the
+         <a href="https://mind.be/buildroot-lts">Buildroot LTS Sponsoring
+         Program</a>.</p>
+      <p>When the Buildroot LTS Sponsoring program will be operational
+         later in 2024, those sponsors will be mentioned here.</p>
+    </div>
+
     <div class="panel panel-primary">
     <div class="panel-heading">Current sponsors</div>
     <div class="panel-body">