Adding a best practice to use HTTPS... or at least have good SSL health?

### Describe the problem

Some transit agencies may still use HTTP request methods to serve GTFS files. Other times, so agencies may have a SSL certificate with bad health. Both of these items may cause problems for data consumers where the request is rejected due to lack of a secure enough connection.

### Use cases

This would happen when data is being requested using HTTP or HTTPS.

### Proposed solution

Add a best practice that recommends using HTTPS with good health of the SSL certificates.

### Additional information

I'm assuming this is very obvious to some people, but it does happen out in the wild.