Create Code Style guidelines / documentation

[SovereignAndrey]

Having a set of code style guidelines would be good to ensure the quality of our web app's code no mate whom is contributing to it, makes our code reviews more objective as we're looking for code that makes a minimum set of criteria, and helps all new comers to get up to speed more quickly.

Consider a simple markdown file in the top level folder of the web app repo.

This could be things like spaces vs tabs, lineending, linters to use, etc. It can also cover things like approches/thoughts to abstraction, interfaces, component structuring and page logic.