Documentation improvements

[jacoscaz]

@megoth has recently been working on adding quadstore to the libraries reviewed on https://rdfjs.dev , as per https://github.com/megoth/rdfjs/issues/6 . Discussion with them suggests the following improvements to quadstore's documentation:

• [ ] Moving the paragraph on how to use quadstore in browsers closer to the top of the README.md file and mention the browser-level in the list of supported backends (from https://github.com/megoth/rdfjs/issues/6#issuecomment-1987160161 ).
• [ ] Point developers looking for ways to parse/serialize RDF to the libraries on https://rdf.js.org (from https://github.com/megoth/rdfjs/issues/6#issuecomment-1999484412)

[jacoscaz]

Done in https://github.com/jacoscaz/quadstore/commit/7e5f3b97317e3b8d3f6adb57408682ecf6fe7d7e and https://github.com/jacoscaz/quadstore/commit/39bc9afbc3f4e18a191e4945766ed75dee8f51bc, respectively.