Update README.md

Author: Edward Thomson

README.md

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 git-recover: recover deleted files in your repository
 ===========
 
+[![CI](https://github.com/ethomson/git-recover/workflows/CI/badge.svg)](https://github.com/ethomson/git-recover/actions?query=workflow%3ACI)
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 `git-recover` allows you to recover some files that you've accidentally deleted
 from your working directory.  It helps you find files that exist in the
 repository's object database - because you ran `git add` - but were never