Improve documentation of TatoebaDownloader

[ynop]

For the parameters of the TatoebaDownloader, a better description is neccessary for where to find, what values are accepted:

audiomate/audiomate/corpus/io/tatoeba.py

Lines 26 to 29 in 14e932c

	include_languages (list): List of languages to download. If None all are downloaded.
	include_licenses (list): Sentences are downloaded only if their license is in this list.
	If None all licenses are included.
	load_empty_license (bool): Sentences with an empty license are not meant to be reused.