Clarify in the docs that URI-embedded query params do not need to be encoded

[phoe]

Docs say:

Note that a query already contained in uri will always be sent with the request line anyway in addition to other parameters sent by Drakma.

That was not clear enough to me. I wasted some time being convinced that query parameters passed directly in the URI need to be manually percent-encoded, as opposed to those passed through :parameters, due to possible ambiguity in URI meaning. :preserve-uri should be possibly mentioned in that paragraph to clarify this case.

Will make a MR for that once I get to this.