Document all GitHub Action inputs

[PaulRBerg]

The README does not document all inputs that this GitHub Action supports, e.g. openai_heavy_model, which is an important setting that allows users to switch between GPT3.5 and GPT4.

[harjotgill]

We have made the gpt-4 model default for now. Hopefully this isn't a cause of confusion now.

[JaredEzz]

I would second a request to document all the action inputs. You can/should specify the defaults, and mark the optional params as such

[harjotgill]

I will appreciate help on this folks! I am a startup CEO (FluxNinja), and this is a side project for me. :)