changing Slack to Discord (#3040)

* changing Slack to Discord

* Update README.md

* updating contributing

CONTRIBUTING.md

@@ -87,7 +87,7 @@ Update API documentation (slow)..........................................Passed
 Note: If you prefer you can run this hook before `git push` instead of `git commit`. To do so, install the hook with `pre-commit install --hook-type pre-push`
 
 Note: pre-commit hooks might fail. If that happens to you and you can't understand why, please do the following:
-- Ask for help by opening an issue or reaching out on our Slack channel. We usually give some feedback within a day for most questions.
+- Ask for help by opening an issue or reaching out on our Discord channel. We usually give some feedback within a day for most questions.
 - As the last resort, if you are desperate and everything failed, ask Git to skip the hook with `git commit --no-verify`. This command will suspend all pre-commit hooks and let you push in all cases. The CI might fail, but at that point we will be able to help.
 - In case of further issues pushing your changes, please uninstall the hook with `pre-commit uninstall -t pre-commit -t pre-push` and review your Git setup.
 

README.md

@@ -62,7 +62,7 @@ Haystack is built in a modular fashion so that you can combine the best technolo
 | :floppy_disk: [Installation](https://github.com/deepset-ai/haystack#floppy_disk-installation) | How to install Haystack |
 | :mortar_board: [Tutorials](https://github.com/deepset-ai/haystack#mortar_board-tutorials) | See what Haystack can do with our Notebooks & Scripts |
 | :beginner: [Quick Demo](https://github.com/deepset-ai/haystack#beginner-quick-demo) | Deploy a Haystack application with Docker Compose and a REST API |
-| :vulcan_salute: [Community](https://github.com/deepset-ai/haystack#vulcan_salute-community) | [Slack](https://haystack.deepset.ai/community/join), [Twitter](https://twitter.com/deepset_ai), [Stack Overflow](https://stackoverflow.com/questions/tagged/haystack), [GitHub Discussions](https://github.com/deepset-ai/haystack/discussions) |
+| :vulcan_salute: [Community](https://github.com/deepset-ai/haystack#vulcan_salute-community) | [Discord](https://haystack.deepset.ai/community/join), [Twitter](https://twitter.com/deepset_ai), [Stack Overflow](https://stackoverflow.com/questions/tagged/haystack), [GitHub Discussions](https://github.com/deepset-ai/haystack/discussions) |
 | :heart: [Contributing](https://github.com/deepset-ai/haystack#heart-contributing) | We welcome all contributions! |
 | :bar_chart: [Benchmarks](https://haystack.deepset.ai/benchmarks/latest) | Speed & Accuracy of Retriever, Readers and DocumentStores |
 | :telescope: [Roadmap](https://haystack.deepset.ai/overview/roadmap) | Public roadmap of Haystack |
@@ -319,7 +319,7 @@ There is a very vibrant and active community around Haystack which we are regula
 If you have a feature request or a bug report, feel free to open an [issue in Github](https://github.com/deepset-ai/haystack/issues).
 We regularly check these and you can expect a quick response.
 If you'd like to discuss a topic, or get more general advice on how to make Haystack work for your project, 
-you can start a thread in [Github Discussions](https://github.com/deepset-ai/haystack/discussions) or our [Slack channel](https://haystack.deepset.ai/community/join).
+you can start a thread in [Github Discussions](https://github.com/deepset-ai/haystack/discussions) or our [Discord channel](https://haystack.deepset.ai/community/join).
 We also check [Twitter](https://twitter.com/deepset_ai) and [Stack Overflow](https://stackoverflow.com/questions/tagged/haystack).