Fixes and improvements for `recognize_assemblyai()` method:

[patrickloeber]

Hi, I made some fixes and improvements for the recognize_assemblyai() method, since it was only working with a file path before and didn't have correct error handling:

• Adds support for AudioData instance. Before, it only worked with a path to a file
• Adds more error handling
• Removes inner read_file function since the requests module automatically handles chunking
• Removes "content-type" from header since this is not needed
• Adds docstring
• Adds example code snippet in examples/audio_transcribe.py
• Lists AssemblyAI in README