chore: mention signed commit requirement (#43406)

chore: mentioned signed commit requirement

.github/config.yml

@@ -2,6 +2,8 @@
 newPRWelcomeComment: |
   💖 Thanks for opening this pull request! 💖
 
+  ### Semantic PR titles
+
   We use [semantic commit messages](https://github.com/electron/electron/blob/main/docs/development/pull-requests.md#commit-message-guidelines) to streamline the release process. Before your pull request can be merged, you should **update your pull request title** to start with a semantic prefix.
 
   Examples of commit messages with semantic prefixes:
@@ -10,6 +12,13 @@ newPRWelcomeComment: |
   - `feat: add app.isPackaged() method`
   - `docs: app.isDefaultProtocolClient is now available on Linux`
 
+  ### Commit signing
+
+  This repo enforces [commit signatures](https://docs.github.com/en/authentication/managing-commit-signature-verification/signing-commits) for all incoming PRs.
+  To sign your commits, see GitHub's documentation on [Telling Git about your signing key](https://docs.github.com/en/authentication/managing-commit-signature-verification/telling-git-about-your-signing-key).
+  
+  ### PR tips
+
   Things that will help get your PR across the finish line:
 
   - Follow the JavaScript, C++, and Python [coding style](https://github.com/electron/electron/blob/main/docs/development/coding-style.md).