Added licence file

[gentlegiantJGC]

This licence is a combination of PolyForm Sheild and Polyform Noncommercial.
Users wanting to use Amulet for commercial purposes must purchase a licence.

[CLAassistant]

All committers have signed the CLA.

[gentlegiantJGC]

Hello contributors to Amulet Map Editor.
We have finally assembled the licence terms for Amulet and want to make you aware of these changes.
The licence terms can be viewed in the files changed section of this pull request.

We are assuming that any contributions made by anyone outside Amulet-Team before signing the Contributor Licence Agreement were made under the terms of the MIT licence.
This means that anyone is able to use and relicense your contributions without having to notify you.
If you have any objections to this please respond below and we will look into removing your contributions.

We will merge this licence on or after 3rd November 2022 to give you a chance to respond if you so wish.

@gentlegiantJGC, @Podshot, @ALTB0ne, @toka7290, @ianz56, @MrFellox, @naor2013, @ezfe, @StealthyExpertX, @Max-RM, @PavelDobCZ23, @IoeCmcomc, @yudonglin, @kolan222, @kqakqakqa, @MarkHalpaap, @Euxcbsks, @GiftShower, @sparks0, @VolchaH, @jerbear2008, @Kraballa, @IcrusaI, @Ex-Ark, @Eiim, @Barteks2x and @ghost

[Eiim]

I definitely prefer the MIT license to this one, but my contributions are so negligible that I don't mind them being re-licensed under this.

[StealthyExpertX]

Yes, it's fine, and thank you for letting us know!

What license will plugins be under if you don't mind me asking?

[gentlegiantJGC]

What license will plugins be under if you don't mind me asking?

This section talks about plugins.
https://github.com/Amulet-Team/Amulet-Map-Editor/pull/669/files#diff-16a761c9aa2fdb48257c9273c4850c265478c132abdea216aba4fa458cc57564R55-R64

In summary you are free to do what you want.
Perhaps we should formalise that more.