[doc] Clarification on the input normalisation format.

[Conchylicultor]

Thank you for sharing the code and models!

If I had a small suggestion, I would recommend to describe the input format in the hub description. Something like: image input should be a float32 scaled around [-1, 1]. This might seems obvious but some models normalize each channel independently with custom mean/std.

I had to dig into the source code to find out how the image was normalized :

big_transfer/input_pipeline_tf2_or_jax.py

Line 107 in 49afe42

im = (im - 127.5) / 127.5