Add Belarusian language support

[wiedymi]

Hi! I would like to translate reactjs.org to belarusian language. This is an official language in Belarus.

[wiedymi]

@tesseralis please, review it.

[SmolinPavel]

@tesseralis could you please review this PR?

[zubialevich]

Hi! Can you add me to the maintainers list?

[zubialevich]

Is it possible to add new locales for translation? Seems bot have some problems #196

[wiedymi]

@zubialevich Hi, I've added you to the maintainers list.

[wiedymi]

@SmolinPavel Please, check this PR again, and if it's possible merge it

[SmolinPavel]

@wiedymi sorry, I don't have permissions to merge. I was just trying to speed up the process of this PR to be merged.

[gaearon]

Hi folks, sorry for no response.

We've been working on new React docs, and so translations of the old site were deprioritized.
In the meantime, it looks like our GitHub permissions sync may have broke.

Now that we've rolled out the new site and reset the repositories for new translations, I'm going to close all old pull requests including this one so that we can start from a clean slate. If you'd like to still make the same change, please open a new PR.

Thanks, and sorry for the churn.