Add more boilerplate/fluff to `.gitignore`

**Is your feature request related to a problem? Please describe.**
The current `.gitignore` is missing a lot of common file system clutter (eg `.DS_Store` on mac) as well as some common python IDE files.

**Describe the solution you'd like**
We should update it. GitHub provides a suggested Python gitignore file.

**Describe alternatives you've considered**
n/a

**Additional context**
n/a
