Add decouple. (#5179)

* Add decouple.

* Improve the description of decouple per the suggestion by Sourcery AI (I for one welcome our new robotic code-review overlords).

README.md

@@ -3119,6 +3119,7 @@ _Plugin for text editors and IDEs._
 ## Go Tools
 
 - [colorgo](https://github.com/songgao/colorgo) - Wrapper around `go` command for colorized `go build` output.
+- [decouple](https://github.com/bobg/decouple) - Find “overspecified” function parameters that could be generalized with interface types.
 - [depth](https://github.com/KyleBanks/depth) - Visualize dependency trees of any package by analyzing imports.
 - [docs](https://github.com/go-oas/docs) - Automatically generate RESTful API documentation for GO projects - aligned with Open API Specification standard.
 - [go-callvis](https://github.com/TrueFurby/go-callvis) - Visualize call graph of your Go program using dot format.