Add an Adopters file to mention who is using boaviztapi

[demeringo]

Problem

We do not know much who is using API.

Solution

• [ ] Add an Adopters file to the repo where user can indicate they or their organization uses the API.
• [ ] Update Readme, docs or contributing guidelines to mention it

See an example on Cloud Carbon Footprint: https://github.com/cloud-carbon-footprint/cloud-carbon-footprint/blob/trunk/ADOPTERS.md