Addition of Russian documentation

[Kostenkov-2021]

This commit adds Russian documentation for users, developers and translators.

[NSoiffer]

I'm very impressed that you are implementing Russian braille! I'd very much like to see at least 100 examples that cover different parts of the braille system. I couldn't find any online spec, but I did see that this Wikipedia page has three examples. I added them to russian.rs. All of them fail. I don't trust that the examples are correct, but even if they aren't correct, the output has non-braille characters and that's clearly wrong. Here's an example:

---- braille::Russian::russian::wikipedia_linear_parens stdout ----
  left: "⠼⠉⠄⠣⠼⠊⠀⠤⠼⠛⠜⠀⠶⠼⠋"
 right: "⠼⠉'\\⠭⠼⠚⠚⠚⠚⠃⠛'(⠼⠊⠀⠤⠼⠛)⠀⠶⠼⠋"' at tests\common\mod.rs:152:0

I'll bring over the documentation into main so it should show up on the web page.

[Kostenkov-2021]

Hello. Thank you for adding documentation. I will continue working on braille. thank you for your feedback.