Add info on crowdsourcing platforms / instructions

[sudodoki]

• platform / link
• default tasks supported + link to instructions on providing custom UI / tasks for annotators
• instructions on injecting/exporting data

[sudodoki]

https://www.mturk.com/
https://www.figure-eight.com/
https://handl.ai/
https://toloka.yandex.ru/

don't know about this one, just found via googling: https://gengo.ai

[sudodoki]

Some of this are not platforms but are built on top of somes
https://aws.amazon.com/sagemaker/groundtruth/
https://www.cromalab.net/LegionTools/
http://www.gethybrid.io/
https://imerit.net/
https://prolific.ac/
https://scale.ai