WFST_tutorial for ITN development (#3128)

* Pushing WFST_tutorial for open draft. (Still need to review collab code.

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* Checked tutorial code for WFST_Tutorial is properly functioning. Also included some formatting edits.

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* Responding to editorial comments for WFST_tutorial

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* Added images to folder and wrote README for tutorials

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* Few more editorial changes to explain permutations in classification.

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* Updated tutorials documentation page.

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* Forgot links for README

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* TOC links were dead

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* More dead links to fix.

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* removing collab install and appending a warning instead.

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* Update WFST_Tutorial.ipynb

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docs/source/starthere/tutorials.rst

@@ -139,3 +139,6 @@ To run a tutorial:
    * - Text Processing
      - Inverse Text Normalization for ASR
      - `Inverse Text Normalization <https://colab.research.google.com/github/NVIDIA/NeMo/blob/stable/tutorials/text_processing/Inverse_Text_Normalization.ipynb>`_
+   * - Text Processing
+     - Constructing Normalization Grammars with WFSTs
+     - `WFST Tutorial <https://github.com/NVIDIA/NeMo/blob/stable/tutorials/text_processing/WFST_Tutorial.ipynb>`_

tutorials/text_processing/README.md

@@ -0,0 +1,24 @@
+# NeMo Text Processing Tutorials
+
+The NeMo Text Processing module provides support for both Text Normalization (TN) and 
+Inverse Text Normalization (ITN) in order to aid upstream and downstream text processing.
+The included tutorials are intended to help you quickly become familiar with the interface
+of the module, as well as guiding you in creating and deploying your own grammars for individual
+text processing needs.
+
+If you wish to learn more about how to use NeMo's for Text Normalization tasks (e.g. conversion
+of symbolic strings to verbal form - such as `15` -> "fifteen"), please see the [`Text Normalization`](https://colab.research.google.com/github/NVIDIA/NeMo/blob/stable/tutorials/text_processing/Text_Normalization.ipynb)
+tutorial.
+
+If you wish to learn more about Inverse Text Normalization - the inverse task of converting 
+from verbalized strings to symbolic written form, as may be encountered in downstream ASR - 
+consult the [`Inverse Text Normalization`](https://colab.research.google.com/github/NVIDIA/NeMo/blob/stable/tutorials/text_processing/Inverse_Text_Normalization.ipynb) tutorial.
+
+For those curious about constructing grammars tailored to specific languages and use cases,
+you may be interested in working through the [`WFST Tutorial`](https://github.com/NVIDIA/NeMo/blob/stable/tutorials/text_processing/WFST_Tutorial.ipynb), which goes through NeMo's Normalization
+process in detail.
+
+As NeMo Text Processing utilizes Weighted Finite State Transducer (WFST) graphs to construct its 
+grammars, a working knowledge of [Finite State Automata](https://en.wikipedia.org/wiki/Finite-state_machine) (FSA) and/or regular languages is suggested.
+Further, we recommend becoming functionally familiar with the [`pynini` library](https://www.openfst.org/twiki/bin/view/GRM/Pynini) - which functions
+as the backend for graph construction - and [Sparrowhawk](https://github.com/google/sparrowhawk) - which NeMo utilizes for grammar deployment.