s/Service/Directory/ in README

Author: emersion

README.md

@@ -2,7 +2,7 @@
 
 [![GoDoc](https://godoc.org/github.com/emersion/go-openpgp-wkd?status.svg)](https://godoc.org/github.com/emersion/go-openpgp-wkd)
 
-A Go library for [OpenPGP Web Key Service](https://tools.ietf.org/html/draft-koch-openpgp-webkey-service-06).
+A Go library for [OpenPGP Web Key Directory](https://tools.ietf.org/html/draft-koch-openpgp-webkey-service-06).
 
 ## License