Add note to description

[rzhao271]

Ref #139247

This PR appends the following sentence to the emmet.useInlineCompletions setting:

To prevent the non-inline completion item provider from showing up as often 
while this setting is `true`, turn `#editor.quickSuggestions#` to 
`inline` or `off` for the `other` item.

An alternative to updating the description is to change the setting itself so it gives the user the option to use the inline completion provider only, but for that case:

1. We'd need to change the setting from a boolean setting to an enum setting and add in enum values and descriptions.
2. We would still have to document the fact that the final behaviour depends a lot on the editor.quickSuggestions setting.