Add new guide documentation

[crandmck]

Per recent discussion, we are going to add some new "guides". This will be the over-arching issue to identify guide topics, discuss, and track the ongoing work. We already have issues for a couple of these, as noted below.

The initial plan is for Rand and Yaapa to write initial drafts that will be reviewed by Doug, Ritchie, et. al. Then we will solicit additional input from the wider community.

Some proposed topics (to be updated as we identify more):

• 5.x Migration Guide: Add 5.x migration guide #453
• Best Practices for using Express in Production: Centralization of production best practices #452
• Writing middleware for use in Express apps Write new guide on creating middleware for use with Express #461

NOTE: These two topics could be covered in the "Best practices in production" article or separately:

• Security Best Practices
• Performance and Scalability Best Practices

Please suggest other topics to add to the queue? @dougwilson

[crandmck]

We have opened separate issues to track work on individual topics, e.g. #461, #463, #466, etc., so I'm going to close this as it doesn't provide any additional value.