Add links to layered standards (#688)

fixes #686

Author: t-sommer

content/_index.html

@@ -109,8 +109,45 @@ <h1 class="mb-4">The leading standard to exchange dynamic simulation models</h1>
   </div>
 </div>
 
+<div class="container mx-auto pb-3 mb-3 mb-md-5 text-md-center">
+
+  <div class="masthead-followup-icon d-inline-block mb-3">
+    <i class="fa-solid fa-layer-group" style="font-size: 50px;"></i>
+  </div>
+  
+  <h2 class="display-5 mb-3 fw-semibold lh-sm">Layered Standards</h2>
+  
+  <p class="lead fw-normal">
+    The following <a href="https://fmi-standard.org/docs/3.0.2/#VersioningLayered">Layered Standards</a> based on FMI are currently under development.
+  </p>
+
+  <div class="d-flex justify-content-center mb-3">
+    <div class="text-start fs-5">
+      <ul style="list-style-type: none; padding: 0;">
+        <li>
+          <a href="https://github.com/modelica/fmi-ls-xcp">XCP</a> — information for calibration and measurement <small class="ms-1 px-2 py-1 text-success-emphasis bg-success-subtle border border-success-subtle rounded-2">released</small>
+        </li>
+        <li>
+          <a href="https://github.com/modelica/fmi-ls-bus">BUS</a> — mapping of variables to buses
+        </li>
+        <li>
+          <a href="https://github.com/modelica/fmi-ls-struct">Struct</a> — semantic grouping of variables
+        </li>
+        <li>
+          <a href="https://github.com/modelica/fmi-ls-ref">REF</a> — stimuli and reference results
+        </li>
+      </ul>
+    </div>
+  </div>
+
+</div>
+
 <div class="container text-md-center mb-5">
 
+  <div class="masthead-followup-icon d-inline-block mb-3">
+    <i class="fa-solid fa-rocket" style="font-size: 50px;"></i>
+  </div>
+
   <div class="col-lg-8 mx-auto mb-5 text-md-center">
     <h2 class="display-5 mb-3 fw-semibold lh-sm">Getting started</h2>
     <p class="lead fw-normal">
@@ -127,6 +164,10 @@ <h2 class="display-5 mb-3 fw-semibold lh-sm">Getting started</h2>
 
 <div class="container text-md-center" style="margin-top: 100px; margin-bottom: 100px;">
 
+  <div class="masthead-followup-icon d-inline-block mb-3">
+    <i class="fa-solid fa-hammer" style="font-size: 50px;"></i>
+  </div>
+
   <div class="col-lg-8 mx-auto mb-5 text-md-center">
     <h2 class="display-5 mb-3 fw-semibold lh-sm">Implement the FMI</h2>
     <p class="lead fw-normal">