Add note about sample format to AttachAudioStreamProcessor()

[AlbertoGP]

Please excuse the noise, I should have included this in the previous PR #3186 instead of asking there whether I should do it. I wasn’t sure whether the buffer passed to AttachAudioStreamProcessor() always used the same type as AttachAudioMixedProcessor() although it looked like that in the example.

I’ve been reading carefully the example for AttachAutdioStreamProcessor() and the source code, and it is now clear to me that this function too uses float for the samples in buffer.

[raysan5]

@AlbertoGP thanks for the addition