add readme

readme.md

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+git-who is an interactive version of git-blame that makes it easy
+to reblame at a previous version and follow a line through commit history
+
+`git who src/git.rs`
+![](https://user-images.githubusercontent.com/90059/237033030-3984c97c-b8b0-4cb4-989b-3b135b22c8ba.png)
+`<Enter>` to follow a line through commit history
+![](https://user-images.githubusercontent.com/90059/237033938-08817c9b-44dd-4313-9ecb-f3ba89890beb.png)
+`<Esc>` or `q`, then `b` to reblame at a previous version
+![](https://user-images.githubusercontent.com/90059/237034888-3785170c-d9d5-4c67-ad6b-3c0411ae0cb3.png)
+`B` will pop the stack and blame at the initial version (first screenshot)