docs: remove obsolete readme.md (#3915)
docs: remove obsolete readme.md (#3915)

this accidentally got pulled in when the kythe/lang-proto repo got merged.
The actual readme for kythe is README.adoc.
kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe