Mention more user account related issues

Add permissions section

Explain how to apply the changes

Mention that creating FxProperties is also useful

Mention that APOs don't involve conversions

Simplify Get-Item command

Typo

Clarify that removing APOs is only for a single endpoint

Explain how to locate a sAPO

Mention pre-mix and post-mix terminology

Explain how to remove sAPOs

Mention PKEY_AudioEndpoint_Disable_SysFx

Describe FxProperties

Describe APOs

Explain how to get the endpoint GUID