Add Supported platforms doc

[acs]

In order to execute McThings we suppport:

• Spigot + https://www.spigotmc.org/resources/raspberryjuice.22724/: Tested with 1.15.2
• Forge (1.12.2) + https://github.com/arpruss/raspberryjammod
• Mintest (5.1) + https://github.com/arpruss/raspberryjammod-minetest

This documentation is critical and must be added to the repository

[acs]

Done!

https://github.com/juntosdesdecasa/mcthings/blob/develop/USAGE.md

This doc is critical for adoption so it is great to have it and we will need to maintain it.

Not entered in a lot of details because for newbies it will be nearly imposible to install all by themselves. We need to think about it. Probably the Minetest option is the easiest one.