Referenced new So implementation.

doc.go

diff --git a/doc.go b/doc.go
index 43ceb6e..5057232 100644
--- a/doc.go
+++ b/doc.go
@@ -82,6 +82,8 @@
 //        log.Println(message)
 //   }
 //
+// For an alternative implementation of So (that provides more flexible return options)
+// see the `So` function in the package at github.com/smartystreets/assertions/assert.
 func So(actual interface{}, assert assertion, expected ...interface{}) (bool, string) {
 	if result := so(actual, assert, expected...); len(result) == 0 {
 		return true, result