Installation instructions in README.rst are out of date

[vollkorn1982]

The installation instructions in https://github.com/davidblewett/rure-python/blob/master/README.rst instruct to set the simd-accel feature for rust::Regex, but starting with version 1.0.1 the SIMD features are automatically activated at runtime: https://github.com/rust-lang/regex/pull/490

I suggest stating in the install instructions that the steps to set simd-accel are only necessary for rust::Regex versions <1.0.1 (2018-06-19).