Please add LICENSE for data

[buriy]

Please add LICENSE.txt for data.
If different data entries have different licenses, please add in the readme.
Thank you.

//by default, no LICENSE means we can't use this data legally for any purpose.

[TatianaShavrina]

Dear @buriy , to be completely precise, every piece of text data has its own license.

• Taiga materials are CC, as well as Syntagrus and wiki + Morphorueval data
• Youtube data and Mokoron Twitter corpus have no legal licence at all, so use them with caution

[buriy]

Syntagrus License: CC BY-NC-SA 4.0 ( according to https://universaldependencies.org/treebanks/ru_syntagrus/index.html )

Youtube data license is usually "Standard Youtube license" (unless it's CC0 license for some texts), and yes it doesn't allow to do anything but through youtube (but fair use rights of course).