[fetch] Document usage for GET requests with URI parameters (#56)

The spec does not document any way to specify GET query parameters (e.g. `search?q=unicorns&limit=10&foobar`) for a request. GET is the most common case but in practice, query parameters may be used with any HTTP method.

As I understand, the way to do this is using  [`URLSearchParams`](https://url.spec.whatwg.org/#urlsearchparams) from the URL spec. It would be good to provide a clearer view of how these two APIs fit together, especially as query strings are often supported directly by the high-level XHR APIs that `fetch` is meant to replace (e.g. jQuery.ajax or reqwest), often as a `data` option for example.

In general, it feels like it would be really great to have a boilerplate-free way to use only native web APIs to do such common things as passing URI parameters.

See also [this Twitter thread](https://twitter.com/tabatkins/status/603564595391762432).

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fetch/issues/56