Add velox logo files and update README.md (facebookincubator#86)

Summary:
Pull Request resolved: facebookincubator#86

Add velox logo files and update README.md to show the logo in the top. Unfortunately, the logo won't show correctly under we land the diff and the new svg files are available in the expected url.

Reviewed By: kgpai

Differential Revision: D30460518

fbshipit-source-id: fef3c9b24cb6e980b1f3301bbb7747374d9b1b38

Author: pedroerp

README.md

@@ -1,4 +1,4 @@
-# velox
+![Velox Logo](https://github.com/facebookincubator/velox/static/logo.svg)
 
 ## Build Notes