feat(services-container): update with example on environment variables

Author: esolitos

en/reference/services-container.html

@@ -555,11 +555,20 @@ <h2 id="nodes">nodes</h2>
 
 <h2 id="environment-variables">environment-variables</h2>
 <p>
-Add children elements to <code>nodes</code> for environment variables - see example below.
-These are set before the services are started on the container node - available for the Container.
+  Allows setting environment variables for the container, those are set before the services are started on the container
+  node.
+  This needs to be a child of <code>nodes</code>. The format is a list of key-value pairs, where the key is the name of
+  the environment variable.
 </p>
-
-
+<p>Example:</p>
+<pre>
+&lt;nodes&gt;
+    &lt;environment-variables&gt;
+        &lt;KMP_SETTING&gt;1&lt;/KMP_SETTING&gt;
+        &lt;KMP_AFFINITY&gt;granularity=fine,verbose,compact,1,0&lt;/KMP_AFFINITY&gt;
+    &lt;/environment-variables&gt;
+    &lt;node/&gt;
+</pre>
 
 <h2 id="jvm">jvm</h2>
 <p>