Improve repository to add option to use it as submodule

[CodeDoctorDE]

Hi,

I want to include this repo as submodule in my project. For this to work, the addons/MaxSizeContainer needs to be top-level.

[MattUV]

I'm not really familiar with plug-in development. Would it still be compatible with the asset library if I don't put everything inside addon/MaxSizeContainer repository?

[CodeDoctorDE]

The scatter plugin uses the same approach: https://github.com/HungryProton/scatter