3 huge issues solved.


@gfosco as #83  signed the `Contributor License Agreement` and reopened   :)

simple modifications:

1. **Absolute link** to relative link, in order to have less maintenance problem on different branches.
2. Usage the PHP section in order to show the **code colored**.
3. **Composer** section in order to help the developer to use this library with composer.

The output will look like: https://github.com/liuggio/facebook-php-sdk/