Add TTS readme detailing HTTP parameters

tts/README.md

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+FakeYou TTS Pipeline
+====================
+
+The following files are entrypoints and an essential part of FakeYou.com functionality: 
+
+* `vocodes_server.py` - Runs as an HTTP server sidecar to the TTS jobs. It loads Tacotron and HifiGan 
+   models into memory and keeps an LRU cache. (The Rust job is responsible for managing which models 
+   are loaded into GPU memory.) Long term it would be better to quantize the models and not stand up 
+   a server to handle requests.
+
+* `vocodes_model_check_tacotron.py` - This checks newly uploaded models to make sure that they have 
+   the expected weights and dimensions. This will block invalid files from being uploaded (eg. video 
+   files).
+
+
+Vocodes Server Parameters
+-------------------------
+
+The `vocodes_server.py` HTTP server accepts HTTP POST requests to the `/infer` endpoint. The requests
+are JSON-encoded and have the following parameters:
+
+* `inference_text` - REQUIRED. The text to convert to speech.
+* `synthesizer_checkpoint_path` - REQUIRED. Where the Tacotron model lives on the filesystem.
+* `vocoder_type` - REQUIRED. Either `hifigan-superres` or `waveglow`.
+* `waveglow_vocoder_checkpoint_path` - OPTIONAL. Where the waveglow vocoder lives on the filesystem. 
+   Inference will use either Waveglow or HifiGan (preferred).
+* `hifigan_vocoder_checkpoint_path` - OPTIONAL. Where the HifiGan vocoder lives on the filesystem. 
+   Inference will use either Waveglow or HifiGan (preferred).
+* `hifigan_superres_vocoder_checkpoint_path` - OPTIONAL. Where the superres HifiGan vocoder lives on the
+   filesystem. This can be used instead of HifiGan.
+* `output_audio_filename` - REQUIRED. The name of the output audio file. This controls where it is saved, 
+   which is important for the code that uploads it to GCP.
+* `output_spectrogram_filename` - REQUIRED. The name of the spectrogram file. This controls where it is saved,
+   which is important for the code that uploads it to GCP.
+* `output_metadata_filename` - REQUIRED. The name of the metadata file. It contains stats such as audio duration.
+   This controls where it is saved, which is important for the code that uploads it to GCP.
+* `maybe_clear_synthesizer_checkpoint_path` - OPTIONAL. Rust can instruct Python to remove models from memory.
+
+This interface between Rust and Python can be changed at any time, of course.
+
+
+TODO
+----
+
+- [ ] Fix `NeMo/` and `nemo/` paths. These do not work on Macs as the filesystem is case-insensitive (ugh).