Обновление online-документации

We’ve just made a serious update of the online documentation of the project. Lots of corrections and typo fixes. And a small but useful theming guide.

The new docs available here: https://docs.mibew.org/

All contents of the documentation licensed under the terms of Creative Commons Attribution-ShareAlike 4.0 International.

The appropriate project hosted at Github: https://github.com/Mibew/docs.mibew.org. And pull requests are still welcome.