Add release artifacts signing to the release process

CONTRIBUTING.md

@@ -649,11 +649,11 @@ should be canceled.
 
 ### Maintainers
 
-- [Damien Mathieu](https://github.com/dmathieu), Elastic
-- [David Ashpole](https://github.com/dashpole), Google
-- [Robert Pająk](https://github.com/pellared), Splunk
-- [Sam Xie](https://github.com/XSAM), Cisco/AppDynamics
-- [Tyler Yahn](https://github.com/MrAlias), Splunk
+- [Damien Mathieu](https://github.com/dmathieu), Elastic ([GPG](https://keys.openpgp.org/search?q=5A126B972A81A6CE443E5E1B408B8E44F0873832)
+- [David Ashpole](https://github.com/dashpole), Google ([GPG](https://keys.openpgp.org/search?q=C0D1BDDCAAEAE573673085F176327DA4D864DC70)
+- [Robert Pająk](https://github.com/pellared), Splunk ([GPG](https://keys.openpgp.org/search?q=CDAD3A60476A3DE599AA5092E5F7C35A4DBE90C2))
+- [Sam Xie](https://github.com/XSAM), Splunk ([GPG](https://keys.openpgp.org/search?q=AEA033782371ABB18EE39188B8044925D6FEEBEA))
+- [Tyler Yahn](https://github.com/MrAlias), Splunk ([GPG](https://pgp.mit.edu/pks/lookup?search=0x46B0F3E1A8B1BA5A))
 
 ### Emeritus
 

RELEASING.md

@@ -112,6 +112,29 @@ It is critical you make sure the version you push upstream is correct.
 Finally create a Release for the new `<new tag>` on GitHub.
 The release body should include all the release notes from the Changelog for this release.
 
+### Sign the Release Artifact
+
+To ensure we comply with CNCF best practices, we need to sign the release artifact.
+The tarball attached to the GitHub release needs to be signed with your GPG key.
+
+Follow [these steps] to sign the release artifact and upload it to GitHub.
+You can use [this script] to verify the contents of the tarball before signing it.
+
+Be sure to use the correct GPG key when signing the release artifact.
+
+```terminal
+gpg --local-user <key-id> --armor --detach-sign opentelemetry-go-<version>.tar.gz
+```
+
+You can verify the signature with:
+
+```terminal
+gpg --verify opentelemetry-go-<version>.tar.gz.asc opentelemetry-go-<version>.tar.gz
+```
+
+[these steps]: https://wiki.debian.org/Creating%20signed%20GitHub%20releases
+[this script]: https://github.com/MrAlias/attest-sh
+
 ## Post-Release
 
 ### Contrib Repository