Add a note about outgrowing Logger

This is a common enough question that it's worth calling out explicitly.

web/middleware/logger.go

@@ -16,6 +16,13 @@ import (
 // print in color, otherwise it will print in black and white.
 //
 // Logger prints a request ID if one is provided.
+//
+// Logger has been designed explicitly to be Good Enough for use in small
+// applications and for people just getting started with Goji. It is expected
+// that applications will eventually outgrow this middleware and replace it with
+// a custom request logger, such as one that produces machine-parseable output,
+// outputs logs to a different service (e.g., syslog), or formats lines like
+// those printed elsewhere in the application.
 func Logger(c *web.C, h http.Handler) http.Handler {
 	fn := func(w http.ResponseWriter, r *http.Request) {
 		reqID := GetReqID(*c)