Unify code signing description

Unified between:
- CONTRIBUTING.md
- https://nvidia.github.io/cuda-python/cuda-core/latest/contribute.html

Author: vzhurba01

CONTRIBUTING.md

@@ -37,9 +37,4 @@ Choose the setup that best fits your workflow and development style.
 
 ## Code signing
 
-This repository implements a security check to prevent the CI system from running untrusted code. A part of the
-security check consists of checking if the git commits are signed. See
-[here](https://docs.gha-runners.nvidia.com/apps/copy-pr-bot/faqs/#why-did-i-receive-a-comment-that-my-pull-request-requires-additional-validation)
-and
-[here](https://docs.github.com/en/authentication/managing-commit-signature-verification/about-commit-signature-verification)
-for more details, including how to sign your commits.
+This repository implements a security check to prevent the CI system from running untrusted code. A part of the security check consists of checking if the git commits are signed. Please ensure that your commits are signed [following GitHub’s instruction](https://docs.github.com/en/authentication/managing-commit-signature-verification/about-commit-signature-verification).