Add instructions for how to freeze + needed changes to support it on Windows

[pushfoo]

JGantts/Storyteller#1 uses a 200 mb dependency in addition to electron. They could use child_process or some sugar library to make this easier if pyc2e can be frozen. Python should be 15-20 mb, an order of magnitude less.

Try pyinstaller if cx_Freeze doesn't work, it doesn't restrict the things it bundles to the GPL .

[pushfoo]

Freezing will need linux, windows, and mac executable versions.

[pushfoo]

Preliminary freezing with pyinstaller seems to work. The caveat is that it doesn't like to run from a virtualenv in a mounted folder in virtualbox. Creating the virtualenv in the windows user's documents folder works as a fix. Afterward, runningpyinstaller D:\pyc2e\__main__.py works but creates a very messy folder.
The result appears to be ~12mb at time of writing.

[pushfoo]

Shipping a single is strongly discouraged for admin mode programs by the pyinstaller documentation:

Do not give administrator privileges to a one-file executable (setuid root in Unix/Linux, or the “Run this program as an administrator” property in Windows 7). There is an unlikely but not impossible way in which a malicious attacker could corrupt one of the shared libraries in the temp folder while the bootloader is preparing it. Distribute a privileged program in one-folder mode instead.

Many users might run this admin mode. Not sure what the best way to proceed is. Need to find out how electron packages dependencies and subcomponents, and compare to cx_Freeze and other tools.
The big advantage of pyinstaller right now is that it doesn't require significant understanding of the framework. pyinstaller path\to\script.py works, even across drive boundaries.