doc(rjy): polish d4pg/ppg/qrdqn policy doc

[nighood]

Description

Related Issue

TODO

Check List

• [ ] merge the latest version source branch/repo, and resolve all the conflicts
• [ ] pass style check
• [ ] pass all the tests

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (d7a61c2) 76.78% compared to head (1db6909) 76.48%. Report is 3 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #762 +/- ## ========================================== - Coverage 76.78% 76.48% -0.30% ========================================== Files 671 676 +5 Lines 53196 53840 +644 ========================================== + Hits 40847 41181 +334 - Misses 12349 12659 +310 ``` | [Flag](https://app.codecov.io/gh/opendilab/DI-engine/pull/762/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opendilab) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/opendilab/DI-engine/pull/762/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opendilab) | `76.48% <100.00%> (-0.30%)` | :arrow_down: | 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=opendilab#carryforward-flags-in-the-pull-request-comment) to find out more.

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