GH#27: Remove README from package data.
GH#27: Remove README from package data.

This change addresses https://github.com/dpranke/pyjson5/issues/27,
where README.md was being included in the source distribution (and in
a bad location, to boot); it is not necessary to include it, since
the contents are in the longdesc field of the package.

dpranke/pyjson5