Document how interactions are matched

[aoberoi]

Description

This is a feature request from #64. The user did not expect that headers were used to match interactions, so this led to thinking there was a bug. We should explicitly document how these interactions are matched.

Requirements (place an x in each of the [ ])

• [x] I've read and understood the Contributing guidelines and have done my best effort to follow them.
• [x] I've read and agree to the Code of Conduct.
• [x] I've searched for any related issues and avoided creating a duplicate issue.