Proposal templates could link back to the PR

For ghc-proposals, the proposal template includes a link back to the PR, which makes it easy to find the canonical place for discussion. Could we do the same here?

For example I was reading https://github.com/simonpj/hf-tech-proposals/blob/ghc-module-naming-2023/proposals/0000-ghc-module-naming.rst and it's not trivial to navigate back to https://github.com/haskellfoundation/tech-proposals/pull/53.