chore(cirrus): update readme to clearly differentiate v1 and v2 api outputs

[relud]

Because

• I was about to link the readme to fxa and I couldn't readily tell which outputs i was looking at

This commit

• Changes the output section headers to specify the api version of the output described, and separates them from the curl examples
• Fixes the incorrectly lower-case Features v2 api output key
• Fixes some v1 api language to not indicate there is a features key in the response

Fixes #github_issue_number