Add a link about deploying at the end of Migrate Guide

[tanberry]

As Austin pointed out, the current Migrate Guide leaves you hanging about the next big step of deploying to production.

See this Slack post:
"I think it would make sense to tack on another section to this Prisma Migrate guide. We take the user through the flow of editing their schema and creating migrations, but we don’t link or reference prisma migrate deploy anywhere.
A simple “Ready to go to production?” with a link to this Migrate deploy guide could be enough. Thoughts?"