Exclude conanfile.py from bare package copy

[jgsogo]

Changelog: Fix: Example bare package recipe excludes conanfile.py from copy
Docs: omit

closes #4829

[danimtb]

As talked, it seems the issue is not that simple and something is messed up with the different input folders of the command

[jgsogo]

Yes, sure, I didn't pay attention to the help message under the --package-folder argument: "it won't call the recipe 'package()' method". I'll try to make it more visible.

[jgsogo]

The error/improvement is in the docs, not in the code.