DotcomShell broken link fix in readme.md (#157)

Fixed the broken link to the DotcomShell readme

Author: kelvinelove

README.md

@@ -12,7 +12,7 @@
 ## Overview
 
 This is a Next.js template utilizing Carbon for IBM.com React, deploying a vanilla instance of Next.js with the
-[DotcomShell](https://github.com/carbon-design-system/carbon-for-ibm-dotcom/blob/main/packages/react/src/components/DotcomShell/README.md),
+[DotcomShell](https://github.com/carbon-design-system/carbon-for-ibm-dotcom/blob/main/packages/react/src/components/DotcomShell/README.stories.mdx),
 along with other various patterns and components available in Carbon for IBM.com.
 
 ## Getting Started