docs: remove Giscus integration (#13138)

Signed-off-by: Anton Gilgur <agilgur5@gmail.com>

docs/overrides/main.html

@@ -2,23 +2,11 @@
 {% block content %}
 {{ super() }}
 
-<!-- Giscus -->
-<h2 id="__comments">{{ lang.t("meta.comments") }}</h2>
+{# Footer #}
+<hr />
 
-<script src="https://giscus.app/client.js"
-        data-repo="argoproj/argo-workflows"
-        data-repo-id="MDEwOlJlcG9zaXRvcnkxMDA5ODI0NDk="
-        data-category="General"
-        data-category-id="MDE4OkRpc2N1c3Npb25DYXRlZ29yeTMyMTA3OTY1"
-        data-mapping="pathname"
-        data-reactions-enabled="1"
-        data-emit-metadata="0"
-        data-input-position="bottom"
-        data-theme="light"
-        data-lang="en"
-        data-loading="lazy"
-        crossorigin="anonymous"
-        async>
-</script>
+<h2>Have a question?</h2>
 
-{% endblock %}
+Search on <a href="https://github.com/argoproj/argo-workflows/discussions?discussions_q=">GitHub Discussions</a> and <a href="https://argoproj.github.io/community/join-slack/">Slack</a>.
+
+{% endblock %}