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

### Is this a new bug?

- [X] I believe this is a new bug
- [X] 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

```markdown
- OS:
- Python:
- dbt-adapter:
```

### Additional Context

_No response_