Add Slack badge and Maven release availability disclaimer

Author: oleg-nenashev

README.md

@@ -1,6 +1,8 @@
 # TestContainers Java module for WireMock
 
-> NOTE: This project is under development.
+[![a](https://img.shields.io/badge/slack-slack.wiremock.org-brightgreen?style=flat&logo=slack)](http://slack.wiremock.org/)
+
+> NOTE: This project is under development, the GitHub Packages release is coming soon.
 > Not all WireMock features are supported at the moment,
 > and there might be incompatible changes before the 1.0 release.
 > Contributions are welcome!