Add deprecation notice (docker-library/bashbrew#17)

Author: tianon

README.md

@@ -1,3 +1,7 @@
+# DEPRECATED
+
+**IMPORTANT NOTE:** this repository has become part of [`github.com/docker-library/bashbrew`](https://github.com/docker-library/bashbrew) (as of [docker-library/bashbrew#17](https://github.com/docker-library/bashbrew/pull/17)).  Please adjust your usage accordingly!
+
 # `import "github.com/docker-library/go-dockerlibrary/manifest"`
 
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