add an explanation of what is a subdomain

pages/parameters/website.vue

@@ -12,7 +12,7 @@
         :model="Parameters"
       >
         <div class="section-header">
-          <div class="flex-grow-1 align-self-center">
+          <div class="flex-grow-1">
             <span>{{ $t('your_website_address_is') }} : </span>
             <strong class="ml-2">
               <a :href="organizationProfile.website ?? '#'" target="_blank">
@@ -53,9 +53,13 @@
 
     <LayoutParametersSection v-if="!parameters.desactivateOpentalentSiteWeb">
       <div class="section-header">
-        <h4 class="flex-grow-1 align-self-center">
+        <h4 class="flex-grow-1">
           {{ $t('your_subdomains') }}
         </h4>
+        <v-img
+          src="/images/help/what_is_a_subdomain.png"
+          width="240px"
+        />
       </div>
 
       <UiLoadingPanel v-if="subdomainsPending" />
@@ -157,12 +161,15 @@ const onAddSubdomainClick = () => {
 
 <style scoped lang="scss">
 .section-header {
-  margin: 10px 0;
+  margin: 12px 0 36px 0;
   display: flex;
-  flex-direction: row;
+  flex-direction: column;
+
+  .v-img {
+    max-width: 240px;
+  }
 
   @media (max-width: 600px) {
-    flex-direction: column;
 
     :deep(.v-btn) {
       height: auto;