How can I install my own plugin written in Ruby?

I tried that one, is very simple. But unfortunately is not working for me.

I tested the same solution in two different apps. Here is the plugin.rb file I used:

# name: auto-email
# about: A super simple plugin to demonstrate how plugins work
# version: 0.0.1
# authors: Xavier Garzon

I also checked my plugins folder in the container (/var/www/discourse/plugins) and it seems that my plugin is not being copied. Maybe that is part of the problem.

For this second test, I also tried:

./launcher rebuild app --clean

and

./launcher restart app

This is the version I’m running:
3.4.0.beta4-dev
(9f41ce7fce)