chore: Fix markdown link formatting in README.md (#1466)

Author: kellertk

README.md

@@ -483,7 +483,7 @@ and passed to this action.
 Versioning
 ----------
 Starting with version 5.0.0, this action uses semantic-style release tags and
-(immutable releases)[https://docs.github.com/en/code-security/supply-chain-security/understanding-your-software-supply-chain/immutable-releases].
+[immutable releases](https://docs.github.com/en/code-security/supply-chain-security/understanding-your-software-supply-chain/immutable-releases).
 A floating version tag (vN) is also provided for convenience: this tag will
 move to the latest major version (vN -> vN.2.1, vM -> vM.0.0, etc.).