crypto: add import comments.

Change-Id: I33240faf1b8620d0cd600de661928d8e422ebdbc
Reviewed-on: https://go-review.googlesource.com/1235
Reviewed-by: Andrew Gerrand <adg@golang.org>

salsa20/salsa/hsalsa20.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // Package salsa provides low-level access to functions in the Salsa family.
-package salsa
+package salsa // import "golang.org/x/crypto/salsa20/salsa"
 
 // Sigma is the Salsa20 constant for 256-bit keys.
 var Sigma = [16]byte{'e', 'x', 'p', 'a', 'n', 'd', ' ', '3', '2', '-', 'b', 'y', 't', 'e', ' ', 'k'}

salsa20/salsa20.go

@@ -19,7 +19,7 @@ This package also implements XSalsa20: a version of Salsa20 with a 24-byte
 nonce as specified in http://cr.yp.to/snuffle/xsalsa-20081128.pdf. Simply
 passing a 24-byte slice as the nonce triggers XSalsa20.
 */
-package salsa20
+package salsa20 // import "golang.org/x/crypto/salsa20"
 
 // TODO(agl): implement XORKeyStream12 and XORKeyStream8 - the reduced round variants of Salsa20.