Remove json profile references

[endolith]

Describe the changes you have made:

• Replace .json profile references with .py: Profiles were changed from .json to .py files in bee3f3c3, but the documentation was not updated everywhere.
• Fix doctest examples format
• Update reference to "Config" which doesn't exist: Possibly related to 4e97cd77
• Clarify comment about default profile: There is no file called default_profile.py. I'm not sure why we would imply that it exists, and allow it to be used, but just clarify the comment for now.

Reference any relevant issues (e.g. "Fixes #000"):

Pre-Submission Checklist (optional but appreciated):

• [ ] I have included relevant documentation updates (stored in /docs)
• [x] I have read docs/CONTRIBUTING.md
• [x] I have read docs/ROADMAP.md

OS Tests (optional but appreciated):

• [ ] Tested on Windows
• [ ] Tested on MacOS
• [ ] Tested on Linux