Add post on proxmox MTU vs VLAN

Signed-off-by: David Young <davidy@funkypenguin.co.nz>

docs/community/slack.md

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+---
+title: Engage with the Geek Cookbook in GitHub
+description: How to use GitHub to interact with the Geek Cookbook community
+icon: fontawesome/brands/slack
+status: new
+---
+
+# How to geek on Slack
+
+## Get yer invite!
+
+Joing a Slack server requires an invite. To get yours, go [here](https://communityinviter.com/apps/funkypenguin/geek-with-us), or use the form below:
+
+<div id="CommunityInviter"></div>
+<script>
+  window.CommunityInviterAsyncInit = function () {
+    CommunityInviter.init({
+      app_url:'geek-with-us',
+      team_id:'funkypenguin'
+   })
+  };
+
+  (function(d, s, id){
+    var js, fjs = d.getElementsByTagName(s)[0];
+    if (d.getElementById(id)) {return;}
+    js = d.createElement(s); js.id = id;
+    js.src = "https://communityinviter.com/js/communityinviter.js";
+    fjs.parentNode.insertBefore(js, fjs);
+  }(document, 'script', 'Community_Inviter'));
+</script>
+
+## Code of Conduct
+
+With the goal of creating a safe and inclusive community, we've adopted the [Contributor Covenant Code of Conduct](https://www.contributor-covenant.org/), as described [here](/community/code-of-conduct/). Use of the Slack server is subject to this code of conduct.
+
+## Spread the love (inviting others)
+
+Invite your co-geeks to Slack by sending them a link to this page, or directly to the [invite generator](https://communityinviter.com/apps/funkypenguin/geek-with-us)
+
+## Formatting your message
+
+See Slack's help page on formatting messages, [here](https://slack.com/help/articles/202288908-Format-your-messages).
+
+!!! tip "Editing your most recent message"
+    You can edit your most-recent message by pushing the up arrow, make your edits, and then push `Enter` to save!
+
+
+--8<-- "common-links.md"