Add Python syntax highlighting in README.md code blocks

[tkoyama010]

Description

Add Python syntax highlighting in README.md code blocks.

Motivation

Small change to highlighting Python code.

Relevant Issues

• None

Changes

• None

New Dependencies

• None

Change Magnitude

patch

Checklist

• You've created an issue with an enhancement label detailing these changes.
• All calculations use S.I. units.
• You've formatted your code using black.
• You've used a line-length of 88.
• All modules, scripts, classes, methods, and functions you've written have
  docstrings.
• Your docstrings use the reStructuredText format.
• Your code is well documented using block comments.
• If you've made any major changes, you've also created new tests in the tests
  package.
• If you use any code or equations from someone else, you've cited your sources in
  a comment or docstring.