Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -2,6 +2,9 @@
 
 Thanks for your interest in contributing! This document contains `nats-io/nats.net` specific contributing details. If you are a first-time contributor, please refer to the general [NATS Contributor Guide](https://nats.io/contributing/) to get a comprehensive overview of contributing to the NATS project.
 
+> [!NOTE]
+> Please make sure to **sign your commits**. All commits must be signed before a _Pull Request_ can be merged.
+
 ## Getting started
 
 There are three general ways you can contribute to this repo:
@@ -32,6 +35,9 @@ A good pull request includes:
 - No more commits than necessary. Sometimes having multiple commits is useful for telling a story or isolating changes from one another, but please squash down any unnecessary commits that may just be for clean-up, comments or small changes.
 - No additional external dependencies that aren't absolutely essential. Please do everything you can to avoid pulling in additional libraries/dependencies as we will be very critical of these.
 
+> [!NOTE]
+> Please make sure to **sign your commits**. All commits must be signed before a _Pull Request_ can be merged.
+
 ## Get Help
 
 If you have questions about the contribution process, please start a [GitHub discussion](https://github.com/nats-io/nats.net/discussions) or join the [NATS Slack](https://slack.nats.io/).