Add Russian translation

[nifadyev]

Translation is adaptive (not word-to-word) and it tries to save the original meaning.

As discussed with @satwikkansal, this translation (and possibly all existing ones) will be stored in folder inside original repository, not in fork. It will give more control because everything will be stored in 1 repository, and it eliminates possible deletion or making translation private.

Please feel free to review this PR. The PR will be periodically updated with new commits. 1 commit — 1 example

Resolves #297