docs: add Discord link to Wiki home page

Also only show relevant help on the Wiki home page

Author: ukkopahis

docs/index.md

@@ -2,12 +2,15 @@
 
 Welcome to the IOTstack Wiki:
 
-* Use the list of contents at the left of this page to explore this Wiki.
-
-	- If you are viewing this on a device that does not show the list by default, click the "≡" icon.
-
-* If you are looking for information on a specific container, click on the "Containers" folder at the bottom of the list.
+* <span class="show-when-wide-layout">
+  Use the header tabs and content list at the left to explore this Wiki.
+  </span>
+  <label class="show-when-narrow-layout">
+  Click the "≡" icon to navigate this Wiki.
+  </label>
 
 * If you are just getting started with IOTstack, see [Getting Started](Basic_setup/).
 
+* You're always welcome to ask questions on the [IOTStack Discord](https://discord.gg/ZpKHnks).
+
 * To contribute see [Contributing](Developers/)

docs/style.css

@@ -1,4 +1,17 @@
+/* vim: set sw=2: */
+
 /* hide "Made with Material" footer */
 .md-footer-meta {
     display: none;
 }
+
+@media screen and (max-width:76.25em) {
+  .show-when-wide-layout {
+    display:none
+  }
+}
+@media screen and (min-width:76.25em) {
+  .show-when-narrow-layout {
+    display:none
+  }
+}