* add ZeroOptimizer to optim

* resolve `duplicate label` warnings

* upgrade docutils && shpinx to resolve `unknown directive or role` warnings

* fix typo

* resolve literal_block && heading warnings

* resolve json literal_block warnings

* resolve python literal_block warnings

* resolve bunches of reference warnings

* resolve bunches of docstring warnings

* resolve warnings in autosummary

* resolve remaining warnings in en docs

* resolve heading warnings in zh_cn docs

* resolve remaining warnings in zh_cn docs

* fix as comments

* fix as comments

* [Docs] Move examples to a new directory

* fix typo

* Doc： update

* update gan

* Doc: update

* init

* init

* Update docs/en/examples/save_gpu_memory.md

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* Update docs/en/examples/save_gpu_memory.md

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* Update docs/en/examples/save_gpu_memory.md

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* Update docs/en/examples/save_gpu_memory.md

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* revise the chinese version on gradiant checkpointing

* Update docs/zh_cn/examples/save_gpu_memory.md

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Qian Zhao <112053249+C1rN09@users.noreply.github.com>

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>
Co-authored-by: Qian Zhao <112053249+C1rN09@users.noreply.github.com>

* [Docs] Translate examples docs

* Update docs/en/examples/resume_training.md

Co-authored-by: Qian Zhao <112053249+C1rN09@users.noreply.github.com>

Co-authored-by: Qian Zhao <112053249+C1rN09@users.noreply.github.com>

* adjust docs structure

* en caption rename

* Update docs/en/index.rst

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* Update docs/en/index.rst

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* Update docs/zh_cn/index.rst

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* [WIP] Refactor-docs-structure

* [Docs] Check link and fix rst  (#498)

* check link

* fix rst

* Fix conf.py

* Fix lint

* minor refine

* minor refine

* modify zh_readme and index.rst

* add migration exampls get_started design to en

* add tutorials to en

* correct chinese doc link

* Apply suggestions from code review

* Update docs/en/advanced_tutorials/distributed.md

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

Co-authored-by: Mashiro <57566630+HAOCHENYE@users.noreply.github.com>