This is a simple plugin that just invokes the radare2 plugin, r2dec (an awesome decompiler), in Binary Ninja. This unfortunately does not preserve any comments or names you've given to variables and functions. Maybe one day...
You must have radare2, r2dec, r2pipe, and pygments installed. Details on installing radare2 can be found here and details on installing r2dec here.
Then to install r2pipe and pygments (python libraries), run:
$ pip install -r requirements.txt --user
Lastly, once radare2 is installed, you must make sure radare2 is in Binary Ninja's PATH. I've commented out two lines in the __init__.py file that you can edit to fix this issue.