Add readme

[GeorgesAlkhouri]

• [x] Prepare Readme file with help texts
  • [x] test browser support
  • [x] check cross-origin stuff in different flavours (Cors Support)
  • [x] describe usually use cases (e.g. to import, to select,...)
  • [x] which RDF formats are supported
  • [x] describe developer-tools/helpers (e.g. log-box, console, ..)

[pietercolpaert]

Please do! And add a project URL to the short description of the repo