style: how does one define new parameters

[DavidSchinazi]

The Concealed auth draft defines new HTTP authentication parameters. Over in https://github.com/httpwg/http-extensions/issues/2801 we realized that the syntax for how to define new parameters and how to refer to those parameters wasn't consistent. I went to check the style guide, and there was no guidance. I picked something consistent for that draft, but it would be good to provide guidance in the style guide, similar to the guidance we provide for header field names.

For what it's worth, what I picked in that draft was:

• when defining a new parameter:

  The REQUIRED "s" (signature) Parameter is an integer that specifies...

• when referencing the parameter:

  The key ID sent in the k Parameter...

Note that "Parameter" is uppercase here, would be good to suggest whether upper- vs lower-case is preferred.

[mnot]

Capitalising "Parameter" may confuse people with Structured Fields terminology; HTTP auth doesn't use SF.

Otherwise looks good.