crypto: add import comments.

Change-Id: I33240faf1b8620d0cd600de661928d8e422ebdbc
Reviewed-on: https://go-review.googlesource.com/1235
Reviewed-by: Andrew Gerrand <adg@golang.org>
diff --git a/otr/otr.go b/otr/otr.go
index d98b323..07ac080 100644
--- a/otr/otr.go
+++ b/otr/otr.go
@@ -4,7 +4,7 @@
 
 // Package otr implements the Off The Record protocol as specified in
 // http://www.cypherpunks.ca/otr/Protocol-v2-3.1.0.html
-package otr
+package otr // import "golang.org/x/crypto/otr"
 
 import (
 	"bytes"