docs: add example for running random command in alias

Fixes #1861

[skip-tests]

docs/_master/_sidebar.md

@@ -46,6 +46,7 @@
 * How To
   * [Phillips Hue](_master/howto/phillipshue.md)
   * [Eval snippets](_master/howto/eval.md)
+  * [Run random command](_master/howto/run-random-command.md)
   * [Write own system](_master/howto/write-own-system.md)
 * Integrations
   * [Twitter](_master/integrations/twitter.md)

docs/_master/howto/run-random-command.md

@@ -0,0 +1,25 @@
+!> You need to have **alias** system enabled
+
+## Example
+
+### Custom variable $_randomCommands
+
+For randomizing commands, you will need to create **eval** custom variable with
+run script set to **When variable is used**
+
+```javascript
+// set of commands
+const commands = [
+    '!me',
+    '!top time',
+    '!points',
+];
+
+// return random command
+return _.sample(commands);
+```
+
+### Alias configuration
+
+Create alias `!youraliashere` with response `$_randomCommands`, this will
+trigger random command.