Adding a note about the related get_pixels() methods on the copy() documentation pages

[villares]

This is a PR attempt based on our discussion here: py5coding/py5generator#624
I hope it helps someone reading the docs... I'm not sure anymore...

I'm unsure about some stylistic details (such as adding a dot to the references of method names...) and about the magical links that pybook likes (no /reference/ at the path to the linked pages, or should I add them?).

This is not very urgent stuff... :)

[hx2A]

Hi @villares , I am going through my inbox and responding to github emails.

To achieve this change, can you make a PR to the relevant files in py5generator?

This file:

https://github.com/py5coding/py5generator/blob/main/py5_docs/Reference/api_en/Py5Graphics_copy.txt

is used to generate the documentation file reference/py5graphics_copy.md you modified in your PR. Same thing for the other two.

The reference documentation pages are not edited directly, they are generated using those reference documentation txt files.

Thanks!