A example tending to mislead

[SeaHOH]

Hi~ Maybe a issue if you want to show unicode escape, this example hardly meets the case.

https://github.com/sqreen/PyMiniRacer/blob/f7b9da0d4987ca7d1982af7f24da423f06da9894/README.rst#L40-L41

In fact Python converted the escape in the example.

Python 2

>>> print(repr(u"'\N{HEAVY BLACK HEART}'"))
u"'\u2764'"

Python 3

>>> print(repr("'\N{HEAVY BLACK HEART}'"))
"'❤'"