Add context on snipping lines

res/welcome.html

@@ -166,6 +166,10 @@ h1::after {
                 <div class="mx_ButtonLabel">_t("Create Account")</div>
             </a>
         </div>
+        <!-- The comments below are meant to be used by Ansible as a quick way
+             to strip out the marked content when desired.
+             See https://github.com/vector-im/riot-web/issues/8622.
+             TODO: Convert to config option if possible. -->
         <!-- BEGIN Ansible: Remove these lines when guest access is disabled -->
         <div class="mx_ButtonRow">
             <div>