New guide: How to create a standalone module / plugin

[Tschakki]

Description

A guide describing how to create a standalone module / plugin.

Motivation

There are some small differences when creating a standalone module / plugin vs an integrated module plugin, which should be outlined and described in the guide. Also, some users might not be aware that they can create standalone plugins/ modules, so it is also a good way to draw their attention to this feature.

Additional information