Document runtime arguments feature

[ss2165]

In Emulator section

[CalMacCQ]

What do you think about making this a subsection of the functions page in the language gude under entrypoint functions? Should also be mentioned in emulator I think.

I think it's important to make clear that this isn't a supported feature on hardware at this stage.

Can also crosslink to the QAOA example as a more involved demo -> https://github.com/Quantinuum/guppylang/blob/main/examples/qaoa_maxcut_example.ipynb