Mention Disks app for changing encryption key in docs

[paulHempel]

https://github.com/system76/docs/blob/master/content/advanced-luks.md
This tutorial only shows the command line way.

The 'Disks' app (which is preinstalled) provides this option as well: select disk > select encrypted partition > settings button > 'change passphrase'.

Therefore my suggestion is to additionally mention the GUI way for non-technical users finding this docs page.

[leviport]

That doc seems like a bit of an oddball. The article description in https://github.com/system76/docs/blob/master/content/password.md mentions changing LUKS passwords, but the article itself does not actually cover that. It might streamline things if we just add a LUKS section to the password.md article, then put this content into that section and get rid of the advanced-luks.md article entirely. @ahoneybun what do you think?

[ahoneybun]

I believe there was some possible data lost with changing it which makes me nervous to even keep it without a disclaimer.

[leviport]

I'm pretty sure that bug was solved long ago.