Mention `dev` packages are not rebuilt default README

Mentioning it in a section of common gotchas might be helpful for others: it's not very easy to guess if one doesnt read carefully all options

Start in the default README and look for a common-gotchas section or the part describing available options. Add a note that dev packages are not rebuilt and explain that this behavior is easy to miss. Done means the README clearly documents this limitation for users who do not read every option closely.

Written by the indexing model from the issue text.