Added some docstrings ops/nn.py

[Frightera]

I added some missing docstrings to the activation functions.

[fchollet]

Thanks for the PR!

[Frightera]

Thanks for the review @fchollet.

Is there any reason both scale and alpha parameters are omitted in selu activation here?

keras-core/keras_core/ops/nn.py

Lines 209 to 212 in db9d734

	def selu(x):
	if any_symbolic_tensors((x,)):
	return Selu().symbolic_call(x)
	return backend.nn.selu(x)

If this is due to a mistake, I can fix it in a separate PR.

[fchollet]

Is there any reason both scale and alpha parameters are omitted in selu activation here

They're not included in the backend ops either. This looks normal.

[Frightera]

@fchollet Thanks for the info. Can you review it once more?

[fchollet]

LGTM, thank you!