Docs: Improve search query routing part on search params

This is a part of https://github.com/nanostores/router/pull/35 but the part that I am confident on. I would have helped me to understand the setup better, with those proposed changes present. However, the part that I did not change here "To use search query like…" which I tried to clarify in https://github.com/nanostores/router/pull/35 is still confusing for me and even this this change here it would have likely lead me to add `search:true`. My suggestion is to merge this part but also improve https://github.com/nanostores/router/pull/35.