Improved coordinate system documentation

[radarhere]

#7155 (comment)

In the docs, it says, for the Coordinate System:

For example, a rectangle covering all of an 800x600 pixel image is written as (0, 0, 800, 600).

Is this not incorrect, as since the images are zero-based, that text ((0, 0, 800, 600)) should actually be for an image 801 x 601? And so that line of text should really be:

For example, a rectangle covering all of an 800x600 pixel image is written as (0, 0, 799, 599).

I've changed the third and fourth items in the tuple to be one less, but I've also changed it to a (2, 2) image instead of (800, 600). I think that's easier to understand.

[Yay295]

Is the upper bound exclusive? (0, 0, 800, 600) would be correct in that case.

[nulano]

I think it depends on the function. #1668/related issues mentioned that both endpoints are included for most ImageDraw functions, but e.g. crop does not seem to include the bottom-right coordinates.

[radarhere]

Good point @nulano

[radarhere]

I'm trying again with #7169, this time by just removing the description of how a rectangle relates to an image.