build(docs): include READMEs from all packages at publish time

[bajtos]

Add a script to copy per-package README files docs/site/readmes, run it as part of the release process.

This enhancement simplifies the process of including new READMEs in the documentation rendered at https://loopback.io, supersedes loopbackio/loopback.io#767 and makes loopback.io's script update-v4-readmes.sh pretty much obsolete.

To keep things simple, I am copying READMEs from almost all packages, even though those READMEs are not used yet. Skipped packages:

• @loopback/docs
• @loopback/benchmark
• everything starting with @loopback/sandbox-

See also #2014 which will greatly benefit from this change.

Checklist

• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• API Documentation in code was updated
• Documentation in /docs/site was updated
• Affected artifact templates in packages/cli were updated
• Affected example projects in examples/* were updated

[b-admike]

LGTM; can we now remove our bash script in favour of this?

[bajtos]

can we now remove our bash script in favour of this?

Yes please! But first we need to publish a new version of @loopback/docs that includes all READMEs.