docs: Use invite link for Discord Server in README (#28)

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## Description

The previous link only works for folks who are already part of the
server. This link should work for anyone, and put them in the
`#fga-general` channel.

## References

Discord discussion:
https://discord.com/channels/759188666072825867/930524706854031421/1133095840676859934

## Review Checklist
- [x] I have clicked on ["allow edits by
maintainers"](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/allowing-changes-to-a-pull-request-branch-created-from-a-fork).
- [ ] I have added documentation for new/changed functionality in this
PR or in a PR to [openfga.dev](https://github.com/openfga/openfga.dev)
[Provide a link to any relevant PRs in the references section above]
- [ ] The correct base branch is being used, if not `main`
- [ ] I have added tests to validate that the change in functionality is
working as expected

README.md

@@ -4,7 +4,7 @@
 [![Release](https://img.shields.io/github/v/release/openfga/dotnet-sdk?sort=semver&color=green)](https://github.com/openfga/dotnet-sdk/releases)
 [![License](https://img.shields.io/badge/License-Apache_2.0-blue.svg)](./LICENSE)
 [![FOSSA Status](https://app.fossa.com/api/projects/git%2Bgithub.com%2Fopenfga%2Fdotnet-sdk.svg?type=shield)](https://app.fossa.com/projects/git%2Bgithub.com%2Fopenfga%2Fdotnet-sdk?ref=badge_shield)
-[![Discord Server](https://img.shields.io/discord/759188666072825867?color=7289da&logo=discord "Discord Server")](https://discord.com/channels/759188666072825867/930524706854031421)
+[![Discord Server](https://img.shields.io/discord/759188666072825867?color=7289da&logo=discord "Discord Server")](https://discord.gg/8naAwJfWN6)
 [![Twitter](https://img.shields.io/twitter/follow/openfga?color=%23179CF0&logo=twitter&style=flat-square "@openfga on Twitter")](https://twitter.com/openfga)
 
 This is an autogenerated SDK for OpenFGA. It provides a wrapper around the [OpenFGA API definition](https://openfga.dev/api).