warning on export feature (#511)

Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>

plugin/src/main/resources/io/jenkins/plugins/casc/ConfigurationAsCode/index.jelly

@@ -1,6 +1,6 @@
 <?jelly escape-by-default='true'?>
 <j:jelly xmlns:j="jelly:core" xmlns:l="/lib/layout" xmlns:f="/lib/form" xmlns:i="jelly:fmt">
-  <l:layout norefresh="true" type="one-column" title="${%about(app.VERSION)}">
+  <l:layout norefresh="true" type="one-column" title="${%Configuration as Code}">
   <l:main-panel>
 
   <div class="container-fluid">
@@ -27,6 +27,8 @@
         </f:form>
 
       </j:otherwise>
+    </j:choose>
+
     <style>
         td {
             vertical-align: middle;
@@ -42,13 +44,19 @@
         </f:bottomButtonBar>
     </f:form>
     <h2>Actions</h2>
+    
     <f:form method="post" action="reload" name="reload">
       <f:submit name="reload" value="Reload existing configuration"/>
     </f:form>
+    <br/>
     <f:form method="post" action="export" name="export">
       <f:submit name="export" value="${%Export Configuration}"/>
+      <div class="alert alert-warning">
+        <img src="${rootURL}/images/16x16/warning.png"/>
+        Export is not intended to offer a directly usable jenkins.yaml configuration. It can be used for inspiration
+        writting your own, be aware export can be partial, or fail for some components.
+      </div>
     </f:form>
-    </j:choose>
 
     <h2>${%Reference}</h2>
     <dt>