GODRIVER-2031 Document that Cursor isn't goroutine safe (#696)

Author: iwysiu

mongo/change_stream.go

@@ -61,7 +61,8 @@ var (
 )
 
 // ChangeStream is used to iterate over a stream of events. Each event can be decoded into a Go type via the Decode
-// method or accessed as raw BSON via the Current field. For more information about change streams, see
+// method or accessed as raw BSON via the Current field. This type is not goroutine safe and must not be used
+// concurrently by multiple goroutines. For more information about change streams, see
 // https://docs.mongodb.com/manual/changeStreams/.
 type ChangeStream struct {
 	// Current is the BSON bytes of the current event. This property is only valid until the next call to Next or

mongo/cursor.go

@@ -21,7 +21,8 @@ import (
 )
 
 // Cursor is used to iterate over a stream of documents. Each document can be decoded into a Go type via the Decode
-// method or accessed as raw BSON via the Current field.
+// method or accessed as raw BSON via the Current field. This type is not goroutine safe and must not be used
+// concurrently by multiple goroutines.
 type Cursor struct {
 	// Current contains the BSON bytes of the current change document. This property is only valid until the next call
 	// to Next or TryNext. If continued access is required, a copy must be made.