Improve documentation on rules for package name

[mebibou]

I don't know if this is the right repository to log this, but the page about the package names doesn't specify the rules for naming a package.

For example, "download" is not allowed. And you can only find this out by trying to publish it, and getting an error in return

[kenshanta]

Package name guidelines
Should be adequate, no?

[mebibou]

Would be a great place to put it, yes. Currently doesn't say anything about not being allowed to name my package @my-namespace/download