Fix Docs

[richp10]

Improve readme docs - especially on correct 'import' statements. This might be something I can help with..

[bkono]

Great idea. Would also be good to get some contributing guidelines in there, as well as docs on how to run the tests. For instance, to confirm my changes I had to stumble through a bit and find the DAT_DRIVER and DAT_DSN env vars for getting the sqlx-runner tests to proceed.