Add note about DbUpX into readme #710
Description
I found DbUpX to be a solution: [https://github.com/fiscaltec/DbUpX](https://github.com/fiscaltec/DbUpX). Instead of a SchemaVersions table, it uses a SchemaVersionHash table, which hashes the contents of each script, so that when a script's content changes, it get re-run.
Edit: figured out how to make a link using Markdown...
Originally posted by @irahsu in #687 (comment)