Add deprecation comment to basic_landing_page template (#2897)

Author: zachbutton

src/site/layouts/basic_landing_page.drupal.liquid

@@ -1,3 +1,11 @@
+{% comment %}
+NOTICE: This template has been migrated to next-build but is not yet released to production.
+Do not make changes here without also updating the corresponding next-build component.
+
+The next-build component can be found here
+https://github.com/department-of-veterans-affairs/next-build/tree/main/src/components/basicLandingPage
+{% endcomment %}
+
 {% include "src/site/includes/header.html" %}
 {% include "src/site/includes/preview-edit.drupal.liquid" %}
 {% include "src/site/includes/breadcrumbs.drupal.liquid" with constructLcBreadcrumbs = true titleInclude = false %}