chore(git-commit-signing): add version warning in README (#377)

Author: phorcys420

git-commit-signing/README.md

@@ -9,6 +9,9 @@ tags: [helper, git]
 
 # git-commit-signing
 
+> [!IMPORTANT]  
+> This module will only work with Git versions >=2.34, prior versions [do not support signing commits via SSH keys](https://lore.kernel.org/git/xmqq8rxpgwki.fsf@gitster.g/).
+
 This module downloads your SSH key from Coder and uses it to sign commits with Git.
 It requires `curl` and `jq` to be installed inside your workspace.