use correct bitgo express quickstart guide URL

Summary: The existing link was throwing a 404

Reviewers: zacleids, luis

Reviewed By: luis

Subscribers: ben

Differential Revision: https://phabricator.bitgo.com/D6155

Author: Alex Melville

README.md

@@ -91,7 +91,7 @@ This ensures your keys never leave your network, and are not seen by BitGo. BitG
 
 `bin/bitgo-express [-h] [-v] [-p PORT] [-b BIND] [-e ENV] [-d] [-l LOGFILEPATH] [-k KEYPATH] [-c CRTPATH]`
 
-For a full tutorial of how to install, authenticate, and use Bitgo Express, see the [Bitgo Express Quickstart](https://platform.bitgo.com/blog/post/bitgo-express-quickstart)
+For a full tutorial of how to install, authenticate, and use Bitgo Express, see the [Bitgo Express Quickstart](https://platform.bitgo.com/bitgo-express/)
 
 # Compile