docs: Document Tokenizer training Pipeline

[MoosaTae]

Why this PR

Why we need this PR?

Changes

• Write some changes here

Related Issues

Close #299

Checklist

• [ ] PR should be in the Naming convention
• [ ] Assign yourself in to Assigneees
• [ ] Tag related issues
• [ ] Constants name should be ALL_CAPITAL, function name should be snake_case, and class name should be CamelCase
• [ ] complex function/algorithm should have Docstring
• [ ] 1 PR should not have more than 200 lines changes (Exception for test files). If more than that please open multiple PRs
• [ ] At least PR reviewer must come from the task's team (model, eval, data)

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (8608ab0) 21.93% compared to head (beb21a7) 21.93%. Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #308 +/- ## ======================================= Coverage 21.93% 21.93% ======================================= Files 19 19 Lines 1231 1231 ======================================= Hits 270 270 Misses 961 961 ``` | [Flag](https://app.codecov.io/gh/OpenThaiGPT/openthaigpt-pretraining/pull/308/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenThaiGPT) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/OpenThaiGPT/openthaigpt-pretraining/pull/308/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenThaiGPT) | `21.93% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenThaiGPT#carryforward-flags-in-the-pull-request-comment) to find out more.

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