Update README for sanity test using Ginkgo.

The original sample is using BeforeEach/AfterEach is a problematic way.

Author: Cheng Pan

pkg/sanity/README.md

@@ -39,21 +39,21 @@ var _ = Describe("MyCSIDriver", func () {
 	Context("Config A", func () {
 		var config &sanity.Config
 
-		BeforeEach() {
-			... setup driver and config...
-		}
+		BeforeEach(func() {
+			//... setup driver and config...
+		})
 
-		AfterEach() {
-			...tear down driver...
-		}
+		AfterEach(func() {
+			//...tear down driver...
+		})
 
 		Describe("CSI sanity", func() {
 			sanity.GinkgoTest(config)
 		})
 	})
 
 	Context("Config B", func () {
-		...
+		// other configs
 	})
 })
 ```