[Wiki] Updating Wiki for Python Idiom Handling

[titomeister]

The skema wiki(https://github.com/ml4ai/skema/wiki/Tree-Sitter-to-CAST-translation) for tree-sitter to CAST to translation needs some updating for how the idiom handling is done in Python. The idea is to document in enough detail that someone new to the project can read it and get started. What's the motivation for doing this? Provide examples on how to test and how to implement idioms. (Think about what one would have to do if they were starting up on a new language).