[DOC] Tokenizer - Letter

[leanneeliatra]

Description

Addition of the Tokenizer - Letter documentation, to the Analyzers section.

Issues Resolved

Part of #1483 addressed in this PR.

Version

all

Frontend features

n/a

Checklist

• By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and subject to the Developers Certificate of Origin.
  For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[github-actions]

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[vagimeli]

@udabhas @varun-lodaya Please provide tech review approval to move this PR forward in the documentation process. Please review this week or provide a peer who can review it. Thank you.

[udabhas]

Looks good to me!