readme & devguide: no longer changing difflink

now that we know how we can get the "xx commits to main since this release back" (re #68; close #68) -- we can just link to that

I didn't update the difflink manually, even when in devguide (wasn't a checklist though). so, good

ReadMe.md

@@ -122,7 +122,7 @@ pkg> add https://github.com/tfiers/PkgGraph.jl#f6e83ca
 [testhist]: https://github.com/tfiers/PkgGraph.jl/actions/workflows/Tests.yml
 
 [commitsimg]:  https://img.shields.io/github/commits-since/tfiers/PkgGraph.jl/latest
-[difflink]:    https://github.com/tfiers/PkgGraph.jl/compare/v0.5.0...main
+[difflink]:    https://github.com/tfiers/PkgGraph.jl/releases/latest
 
 [devdocs-img]: https://img.shields.io/badge/📕_Documentation-dev-blue.svg
 [devdocs]:     https://tfiers.github.io/PkgGraph.jl/dev

docs/src/devguide.md

@@ -26,7 +26,6 @@
   - This will also trigger a DocBuild run, creating a new directory for the tagged
     version on the gh-pages branch.
 - If this is the first release, update the 'Installation' section of the [ReadMe] again.
-- Also in the ReadMe, update the git tag of the latest release in `[difflink]: …`.
 - Remove the temporary warning and PR link.
 
 [`Project.toml`]: https://github.com/tfiers/PkgGraph.jl/edit/main/Project.toml