Update README.md

Murray-LIANG · web-flow · commit 4869c7b29dd8 · 2017-03-31T10:17:06.000+08:00
Bold the `IMPORTANT NOTE` line.
diff --git a/README.md b/README.md
@@ -1,7 +1,7 @@
 Dell EMC Unity Cinder driver
 ============================
 
-##IMPORTANT NOTE:
+## IMPORTANT NOTE:
 
 **Please follow the [Driver configuration](#driver-configuration)
 exactly if you are upgrading Unity Cinder driver from version 0.4.1
