[MacOS] Add disclaimer regarding networks behind user/pass authentication

[seffs]

Hi there,

I realized why this was not working on my MBP...

Networks that require a user/pass authentication will be saved as "802.1X Password" instead of "AirPort network password".
It may not be a good idea to support such a usecase. After all, those kind of logins have a purpose.

Maybe a little disclaimer on the README.md would be beneficial for anyone behind such a network config, thus not wasting time tinkering with low-level commands :(