Document the Deband shader

[Eckoa]

I noticed that vkbasalt can do debanding but there is no documentation on configuring it. I managed to suss out the detail by referencing the reshade deband 2.0 and looking through the shader here. These are likely not formatted in a nice way and could be cleaned up.

I stole the values from reshade and tweaked them very slightly to be between the old and new values that shader used before switching to the latest version.

#Threshold for the difference between the average of reference pixel values 
#and the original pixel value. 
#Higher numbers increase the #debanding strength but progressively diminish image details
#Values are between 0.0 and 255.0
debandAvgdiff = 2.0

#Threshold for the difference between the maximum difference of one of the reference pixel values 
#and the original pixel value.
#Higher numbers increase the debanding strength but progressively diminish image details.
#Values are between 0.0 and 255.0
debandMaxdiff = 4.0

#Threshold for the difference between the average of diagonal reference pixel values 
#and the original pixel value. 
#Higher numbers increase the debanding strength but progressively diminish image details
#Values are between 0.0 and 255.0
debandMiddiff = 3.0

#The radius increases linearly for each iteration. 
#A higher radius will find more gradients, but a lower radius will smooth more aggressively.
#Values are between 1.0 and 32.0
debandRange = 20

#The number of debanding steps to perform per sample. 
#Each step reduces a bit more banding, but takes time to compute.
#Values are 1 to 4
debandIterations = 1