docs: clarify GPG-signed commits are required for wiki contributions

Update contributing/start.md to explicitly state that GPG-signed commits are a requirement for the wiki repository, not just a recommendation. Added a link to setup instructions for configuring GPG signing in git.

Author: johnny603

docs/contributing/start.md

@@ -48,6 +48,8 @@ It is highly recommended that you fill out the "SSH & GPG Keys" tab. Your ssh
 keys should sync to both the [Rocky Linux GitLab](https://git.rockylinux.org) and
 [RESF Git Service](https://git.resf.org).
 
+It is **required** that you add your GPG key to your account, as all commits to the wiki repository must be GPG signed. This is enforced for all contributions. If you have not set up GPG signing for your git commits, please follow the [GitHub guide to signing commits](https://docs.github.com/en/authentication/managing-commit-signature-verification/signing-commits) or refer to your platform's documentation.
+
 It is highly recommended that you add an OTP to your account.
 
 ### Signing Agreements