x/crypto/*: add import comment

Add import comment for blake2b, blake2s, chacha20poly1305 and cryptobyte.

Change-Id: I4703b5cd669e43a5d81422b2ded8b8f54eee5f9b
Reviewed-on: https://go-review.googlesource.com/39952
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

blake2b/blake2b.go

@@ -4,7 +4,7 @@
 
 // Package blake2b implements the BLAKE2b hash algorithm as
 // defined in RFC 7693.
-package blake2b
+package blake2b // import "golang.org/x/crypto/blake2b"
 
 import (
 	"encoding/binary"

blake2s/blake2s.go

@@ -4,7 +4,7 @@
 
 // Package blake2s implements the BLAKE2s hash algorithm as
 // defined in RFC 7693.
-package blake2s
+package blake2s // import "golang.org/x/crypto/blake2s"
 
 import (
 	"encoding/binary"

chacha20poly1305/chacha20poly1305.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // Package chacha20poly1305 implements the ChaCha20-Poly1305 AEAD as specified in RFC 7539.
-package chacha20poly1305
+package chacha20poly1305 // import "golang.org/x/crypto/chacha20poly1305"
 
 import (
 	"crypto/cipher"

cryptobyte/string.go

@@ -5,7 +5,7 @@
 // Package cryptobyte implements building and parsing of byte strings for
 // DER-encoded ASN.1 and TLS messages. See the examples for the Builder and
 // String types to get started.
-package cryptobyte
+package cryptobyte // import "golang.org/x/crypto/cryptobyte"
 
 // String represents a string of bytes. It provides methods for parsing
 // fixed-length and length-prefixed values from it.