Document how to `git bisect` a bug

Along this scratch:

If you know an older version – no matter if release or develop – of PyInstaller worked for you, you can "bisect" to find out which change (commit) causes the error. "Bisecting" is easy, all you need is a development setup for PyInstaller and git.

Let's assume commit 12345678 worked for you then run

git bisect start
git bisect bad            # Current version is bad
git bisect good 12345678  # 12345678 is known to be good

Git will now checkout some next version to test, you need to test you program and run git bisect good or git bisect bad, depending on if you program worked.

To automate this, you can adopt the following script to your needs, save it as run-bisect.sh and run git bisect run sh ./run-bisect.sh.

#!/usr/bin/bash
COMPILE_BOOTLOADER=
if [ -n "$COMPILE_BOOTLOADER" ] ; then
    cd bootloader
    ./waf --no-lsb all
    cd -
fi
pyinstaller --noconfirm my-app.py
dist/my-app/my-app
exit $?

Start with the existing scratch text and the PyInstaller development setup described in the issue. Document the manual git bisect commands and the optional run-bisect.sh automation, including how to judge each tested version; the work is done when a user can follow the instructions to identify a problematic commit.