Update the forum link in the README file

Update the forum link in the readme file as well.
diff --git a/README.md b/README.md
index a2c3c6f..ced36e1 100644
--- a/README.md
+++ b/README.md
@@ -211,7 +211,7 @@
 
 ### Making a Contribution
 
-1.  [Check for open issues](https://github.com/ARMmbed/mbedtls/issues) or [start a discussion](https://tls.mbed.org/discussions) around a feature idea or a bug.
+1.  [Check for open issues](https://github.com/ARMmbed/mbedtls/issues) or [start a discussion](https://forums.mbed.com/c/mbed-tls) around a feature idea or a bug.
 2.  Fork the [Mbed TLS repository on GitHub](https://github.com/ARMmbed/mbedtls) to start making your changes. As a general rule, you should use the "development" branch as a basis.
 3.  Write a test which shows that the bug was fixed or that the feature works as expected.
 4.  Send a pull request and bug us until it gets merged and published. Contributions may need some modifications, so work with us to get your change accepted. We will include your name in the ChangeLog :)