Signed commits comment (#39)

# What 💻 
- Fix #35

# Why ✋
* Adds info about signed commits

# Evidence 📷
Include screenshots, screen recordings, or `console` output here
demonstrating that your changes work as intended

<!-- All sections below are optional. You can uncomment any section
applicable to your Pull Request. -->

<!-- # Notes 📝
* Any notes/thoughts that the reviewers should know prior to reviewing
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---------

Co-authored-by: Sabrina Ferguson <[email protected]>

content/00.build/90.contributing-to-documentation/20.contribution-guidelines.md

@@ -7,15 +7,23 @@ description: Learn how to contribute to ZKsync Docs
 
 **Production**: Visit [ZKsync Docs](https://docs.zksync.io/) for official documentation.
 
-**Staging**: Test and preview changes on the
-[ZKsync Docs Staging](https://zksync-docs-staging-5eb09.web.app/) environment.
+**Staging**: [zKsync Docs Staging](https://staging-docs.zksync.io/) environment.
 
 ## Git workflow
 
 - The `main` branch reflects the current production state.
 - The `staging` branch is for previews in the staging environment.
 - Contributors submit feature branches as PRs to the `staging` branch.
 
+### Signed git commits
+
+Your git commits need to be signed with a verified signature.
+
+1. Follow the instructions to
+  [generate a signing key](https://docs.github.com/en/authentication/managing-commit-signature-verification/generating-a-new-gpg-key).
+1. [Add the key to your GitHub account](https://docs.github.com/en/authentication/managing-commit-signature-verification/adding-a-gpg-key-to-your-github-account).
+1. [Tell git about your signing key](https://docs.github.com/en/authentication/managing-commit-signature-verification/telling-git-about-your-signing-key).
+
 ## Contribution workflow
 
 To set up and run the project locally, consult the root [`README.md`](%%zk_git_repo_zksync-docs%%) file.