README: link to use .../tags instead of ../releases
README: link to use .../tags instead of ../releases

Using github "release" function means that the changelog is buried in the
github webinterface. The changelog is now instead included in README.md.

rfjakob/gocryptfs,davesteele/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs,davesteele/gocryptfs,davesteele/gocryptfs