Improve concurrency doc.

redis/doc.go

@@ -99,10 +99,12 @@
 //
 // Concurrency
 //
-// Connections support a single concurrent caller to the write methods (Send,
-// Flush) and a single concurrent caller to the read method (Receive). Because
-// Do method combines the functionality of Send, Flush and Receive, the Do
-// method cannot be called concurrently with the other methods.
+// Connections do not support concurrent calls to the write methods (Send,
+// Flush) or concurrent calls to the read method (Receive). Connections do
+// allow a concurrent reader and writer.
+//
+// Because the Do method combines the functionality of Send, Flush and Receive,
+// the Do method cannot be called concurrently with the other methods.
 //
 // For full concurrent access to Redis, use the thread-safe Pool to get and
 // release connections from within a goroutine.