add muffet and alternatives (#5402)

README.md

@@ -542,6 +542,7 @@ _Tools for help with continuous integration._
 - [gomason](https://github.com/nikogura/gomason) - Test, Build, Sign, and Publish your go binaries from a clean workspace.
 - [gotestfmt](https://github.com/GoTestTools/gotestfmt) - go test output for humans.
 - [goveralls](https://github.com/mattn/goveralls) - Go integration for Coveralls.io continuous code coverage tracking system.
+- [muffet](https://github.com/raviqqe/muffet) - Fast website link checker in Go, see [alternatives](https://github.com/lycheeverse/lychee#features).
 - [overalls](https://github.com/go-playground/overalls) - Multi-Package go project coverprofile for tools like goveralls.
 - [roveralls](https://github.com/LawrenceWoodman/roveralls) - Recursive coverage testing tool.
 - [woodpecker](https://github.com/woodpecker-ci/woodpecker) - Woodpecker is a community fork of the Drone CI system.