Update Readme to display well on Github

Hi, Michel

You said yesterday you would be interested in what was the Markdown code that didn't parse.  It is really minor.  You can see the example at the top of <https://github.com/rdancer/php-smartypants/tree/0b3fefe48b52f711843dfab6fba07be2e1e2f6fc>; if you search for the string "like this", you will see it.

You said that you didn't want to rename the files, so I've reverted that.

Kind regards
Jan

--

When a code span contains backticks, GitHub Flavoured Markdown[1] would not parse it properly unless the surrounding backticks are doubled, or even tripled.  Example:

    Bad :   (1) ` `a` `     (2) ` ``b'' `
    Good:   (1) `` `a` ``   (2) ``` ``b'' '''

 [1]: https://help.github.com/articles/github-flavored-markdown