Add missing pull request links

Author: aaron-lane

CHANGELOG.md

@@ -75,5 +75,14 @@ and this project adheres to [Semantic Versioning][semver-site].
 [0.3.0]: https://github.com/terraform-google-modules/terraform-google-network/compare/v0.2.0...v0.3.0
 [0.2.0]: https://github.com/terraform-google-modules/terraform-google-network/compare/v0.1.0...v0.2.0
 [0.1.0]: https://github.com/terraform-google-modules/terraform-google-network/releases/tag/v0.1.0
+[#40]: https://github.com/terraform-google-modules/terraform-google-network/pull/40
+[#29]: https://github.com/terraform-google-modules/terraform-google-network/pull/29
+[#27]: https://github.com/terraform-google-modules/terraform-google-network/pull/27
+[#26]: https://github.com/terraform-google-modules/terraform-google-network/pull/26
+[#23]: https://github.com/terraform-google-modules/terraform-google-network/pull/23
+[#19]: https://github.com/terraform-google-modules/terraform-google-network/pull/19
+[#14]: https://github.com/terraform-google-modules/terraform-google-network/pull/14
+[#13]: https://github.com/terraform-google-modules/terraform-google-network/pull/13
+[#6]: https://github.com/terraform-google-modules/terraform-google-network/pull/6
 [keepachangelog-site]: https://keepachangelog.com/en/1.0.0/
 [semver-site]: https://semver.org/spec/v2.0.0.html