Added logo to README
Added logo to README

Had to resort to HTML instead of Markdown in order to constraint the image size *sad panda*

RxSwiftCommunity/rxswiftcommunity.github.io,thanegill/rxswiftcommunity.github.io,RxSwiftCommunity/rxswiftcommunity.github.io,RxSwiftCommunity/rxswiftcommunity.github.io,thanegill/rxswiftcommunity.github.io