Adding logo to README.
Adding logo to README.

davharris/retriever,davharris/retriever,embaldridge/retriever,henrykironde/deletedret,henrykironde/deletedret,bendmorris/retriever,goelakash/retriever,goelakash/retriever,embaldridge/retriever,bendmorris/retriever,davharris/retriever,embaldridge/retriever,bendmorris/retriever