Implement "How it works" page

Mockups

https://www.sketch.com/s/b15c99e6-5cdb-45a6-aba7-92ab5d9d812a/a/ev2bLm/play

https://www.sketch.com/s/c8a846a2-578c-4ed6-8933-553593021ce5/a/vYkEAe