docs: add new documentation URL and new Slack URL in the README
+<div align="left">
+<a href="https://join.slack.com/t/substra-workspace/shared_invite/zt-1fqnk0nw6-xoPwuLJ8dAPXThfyldX8yA"><img src="https://img.shields.io/badge/chat-on%20slack-blue?logo=slack" /></a> <a href="https://docs.substra.org/"><img src="https://img.shields.io/badge/read-docs-purple?logo=mdbook" /></a>
+<br /><br /></div>
+
<div align="center">
<img src="substra_horizontal-color.svg" width="600"/>
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Substra is a python library and a command line interface to interact with the Substra platform.
-For more information on what is substra and how to use is, please refer to the [user documentation](https://connect-docs.owkin.com/en/stable/).
+For more information on what is substra and how to use it, please refer to the [user documentation](https://docs.substra.org/).
-To discuss on Slack, please join the [substra-general](https://lfaifoundation.slack.com/#substra-general) channel and the [substra-help](https://lfaifoundation.slack.com/#substra-help) channel.
+Join the discussion on [Slack](https://join.slack.com/t/substra-workspace/shared_invite/zt-1fqnk0nw6-xoPwuLJ8dAPXThfyldX8yA)!
## Contributing
