docs: clarify override behavior and document FIFO support by theskumar · Pull Request #610

docs: clarify override behavior and document FIFO support by theskumar · Pull Request #610 · theskumar/python-dotenv

- Explicitly state that override=False is the default behavior in the
  Getting Started section for better clarity
- Add note about FIFO (named pipes) support on Unix systems in the
  File format section
- Improve formatting consistency:
  - Standardize TOC list markers (use '-' instead of '*')
  - Fix line wrapping and spacing issues throughout