Broken links in pull request issue template

[MaulingMonkey]

Describe the bug

These links:

* [ ] I have read the [Contributor Guide](../../CONTRIBUTING.md)
* [ ] I have read and agree to the [Code of Conduct](../../CODE_OF_CONDUCT.md)

https://github.com/EmbarkStudios/cargo-about/blame/main/.github/pull_request_template.md#L3-L4

Take me to these broken/404 URLs, when clicked on from a pending pull request such as https://github.com/EmbarkStudios/cargo-about/compare/main...MaulingMonkey:pr-output-file?expand=1:

• https://github.com/EmbarkStudios/CONTRIBUTING.md
• https://github.com/EmbarkStudios/CODE_OF_CONDUCT.md

Working links include:

• https://github.com/EmbarkStudios/cargo-about/blob/main/CONTRIBUTING.md
• https://github.com/EmbarkStudios/cargo-about/blob/main/CODE_OF_CONDUCT.md

Although perhaps linking to the upstream template would be more appropriate?

• https://github.com/EmbarkStudios/opensource-template/blob/main/CONTRIBUTING.md
• https://github.com/EmbarkStudios/opensource-template/blob/main/CODE_OF_CONDUCT.md