Warn when copying too many files

[royra]

When a user copies too many files, they probably have a mounted volume with node_modules (or other vendor directory).

Warn when this happens and suggest a way to create a Compose file for Preevy which doesn't have the mounts.

Should probably have a section in the docs with detailed how-to.

[mihir1739]

Can I work on this?

[royra]

@mihir1739 issue needs a more detailed spec before implementing.