Update readme

[daangeijs]

Now:
trolley = Trolley(searcher=Mint(session, "https://server/mint"),
wado=Wado(session, "https://server/wado"]))

Should be changed to:
trolley = Trolley(searcher=Mint(session, "https://server/mint"),
downloader=Wado(session, "https://server/wado"]))

[Sjoerd Kerkstra]

Thanks for the heads-up! Fixed in a08ae34