[Feature] improve repo's top-level README.md

[dataders]

Is this a new bug?

• I believe this is a new bug
• I have searched the existing issues, and I could not find an existing issue for this bug

Current Behavior

• the title of the README is: dbt-tests-adapter
• the body make no mention of dbt-tests-adapter

additionally there's not install instructions or MAKEFILE

Expected Behavior

it wouldn't be like this #232 is my initial riff on improving

Steps To Reproduce

look at README

Relevant log output

No response

Environment

- OS:
- Python:
- dbt-adapter:

Additional Context

No response