That is directly below the Usage section in the readme.
Hotkey Usage:
-------------
Starting with v1.40, you can set a hotkey in the wsf.ini file. The key you
wish to use must be in regular integer format. Here are some simple
instructions to get started:
1) Start Widescreen Fixer.
2) Exit Widescreen Fixer (This creates the wsf.ini file).
3) Edit the wsf.ini file.
4) Modify the Hotkey= field of the wsf.ini file.
To start off, the default semi-colon hotkey is 186 (0xBA).
If you would like to use the asterik instead, set the number to 106 (0x6A).
So you should have this if you want to user the asterik:
Hotkey=106
The application must not be running when you make the changes or it will over-
write any change you made when you exit.
There's an included Hotkeys.txt that give you the numbers for the most common keys.
If you have any other questions, let me know.