Add note about yaml `!` in disk selection

[rothgar]

Make a not that diskSelector needs quotes when using special characters.

siderolabs/talos#11022

[Iheanacho-ai]

@rothgar I dont think this is solely diskSelector issue, I think this is a YAML issue in general

[rothgar]

Correct, it's an issue with the YAML parser trying to interpret the special characters. This will have more impact than just disk selection but should probably be noted on any page that has advanced filtering (eg network config)