docs: Comparison with PyInstaller is inaccurate

Nobody has claimed this yet.

The [comparison document](https://github.com/indygreg/PyOxidizer/blob/main/docs/comparisons.rst#pyinstaller) states:

> PyInstaller - like PyOxidizer - can produce a self-contained executable file containing your application. However, at run-time, PyInstaller will extract Python source/bytecode files to a temporary directory then import modules from the filesystem. PyOxidizer typically skips this step and loads modules directly from memory using zero-copy. This makes PyOxidizer executables significantly faster to start.

This is only true for onefile mode in PyInstaller, onedir mode does not need to extract any files. The Python modules are directly zip imported from the resulting binary and shared libraries are placed in the directory beside the executable. The onedir mode is actually the default so unless users explicitly opt into it, they will not see this behaviour.

Open docs/comparisons.rst at the PyInstaller comparison and verify the stated runtime behavior against PyInstaller's onefile and onedir modes. Done means the comparison accurately distinguishes extraction in onefile mode from onedir's behavior and notes which mode is the default.

Written by the indexing model from the issue text.