Add packaging configuration

[43081j]

Currently an npm pack or publish will produce unexpected results.

We should add a files entry to our package.json to define what should be packed:

• lib/
• docs/
• README.md

at least.

[stramel]

WDYT about using @pick/pack?

[43081j]

usually i'd be up for it but being that this heavily relies on a commonjs peer dep (eslint), we don't have much use for any other output format so would just be introducing overhead.

i suggest we simply have the files array for now and if eslint ever gets off cjs we consider something like pack.