docs(npmrc): add example of URI fragment limitations

[misse]

Attempt to clarify limitations of how URI Fragments are not applied at the host level but at the path level and are not recursively applied to any sub-path.

When attempting to generate valid npmrc configuration files by using //host.name/:_auth=$token to cover any registry available at that host, I could not get npm to use those credentials.

I figured out the hard way that npm would only use the credentials if I specified the entire path up to the registry name i.e. //host.name/artifactory/api/npm/:auth=$token.

I felt the docs could be clarified to help other users realise the same.

Note: This PR replaces #8095 since I messed up the git commits and were unable to clean it up.

[wraithgar]

I think the disconnect here is that this has less to do with the host/path and more to do with the registry config value. I think the section just above this example is not clearly outlining this. There is a 1:1 relationship between the registry configs, and the 'nerf-darted' uris of auth config.