fix(docs): Update README.md (#1295)

Summary:
### Changes

- [x] Aligning header elements to the center.
- [x] Added logo

> This makes the docs look symmetrical and looks a bit catchy.

Pull Request resolved: https://github.com/facebook/infer/pull/1295

Reviewed By: martintrojer

Differential Revision: D24330220

Pulled By: jvillard

fbshipit-source-id: 1ebb3a997

README.md

@@ -1,9 +1,10 @@
+<img src="website/static/img/logo.png" alt="logo" width="15%" />
+
 # Infer [![Build Status](https://travis-ci.org/facebook/infer.svg?branch=master)](https://travis-ci.org/facebook/infer)
 
 [Infer](http://fbinfer.com/) is a static analysis tool for Java,
 C++, Objective-C, and C. Infer is written in [OCaml](https://ocaml.org/).
 
-
 ## Installation
 
 Read our [Getting