Docs: Extend search params section

Following the advice from https://github.com/nanostores/router/issues/34#issuecomment-2118444983 I was trying to clarify the search params section of the readme. Changes include - Using the term "url search params" which what they are called in https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams/URLSearchParams - Make the default case a bit more obvious by adding the corresponding `createRouter` - Clarify that the `search:true` disables something, not enables something, BUT… … I still don't quite understand what the usecase for `search:true` is and how it would be used in an app. I tried to use it in my app but failed to get something working that made sense. This is my I mark this as a draft for now until this part is improved. I also don't understand what "Parameters order will be critical." means. "Critical" in what way?