add gopher slack invite link

README.md

@@ -41,7 +41,7 @@ Microsoft Azure credits for open source projects
 ## Getting Involved
 [![Slack](https://img.shields.io/badge/slack-Gopher_%23oauth2--proxy-red?logo=slack)](https://gophers.slack.com/archives/CM2RSS25N)
 
-Join the #oauth2-proxy [Slack channel](https://gophers.slack.com/archives/CM2RSS25N) to chat with other users of oauth2-proxy or reach out to the maintainers directly.
+Join the #oauth2-proxy [Slack channel](https://gophers.slack.com/archives/CM2RSS25N) to chat with other users of oauth2-proxy or reach out to the maintainers directly. Use the [public invite link](https://invite.slack.golangbridge.org/) to get an invite for the Gopher Slack space.
 
 OAuth2-Proxy is a community-driven project. We rely on the contribut️ions of our users to continually improve it. While review times can vary, we appreciate your patience and understanding. As a volunteer-driven project, we strive to keep this project stable and might take longer to merge changes.