Docstrings for SpeechRecognitionData

[ethanwharris]

What does this PR do?

Part of #957

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[codecov]

Codecov Report

Merging #1097 (b9077cc) into master (a040936) will increase coverage by 0.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1097      +/-   ##
==========================================
+ Coverage   88.01%   88.13%   +0.12%     
==========================================
  Files         281      281              
  Lines       12807    12819      +12     
==========================================
+ Hits        11272    11298      +26     
+ Misses       1535     1521      -14     

Flag	Coverage Δ
unittests	88.13% <100.00%> (+0.12%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flash/audio/speech_recognition/cli.py	100.00% <ø> (ø)
flash/audio/speech_recognition/data.py	100.00% <100.00%> (+13.33%)	⬆️
flash/audio/speech_recognition/input.py	98.78% <100.00%> (+12.53%)	⬆️
flash/core/data/utilities/samples.py	100.00% <100.00%> (ø)

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[tchaton]

Beautiful work!