Fix UnicodeDecodeError on arm64/aarch64

[hugovk]

Fixes #434

Changes proposed in this pull request:

• The README now contains non-ASCII characters (Update code samples in README #427)
• Therefore explicitly specify UTF-8 when opening the file

The docs https://docs.python.org/3/library/functions.html#open say:

In text mode, if encoding is not specified the encoding used is platform dependent: locale.getpreferredencoding(False) is called to get the current locale encoding.

On a Mac, it's UTF-8, no problem.

On arm64/aarch64, it's ANSI_X3.4-1968.