RL workflows and env sampler doc in RST (#468)

* First rough draft

* Minors

* Reformat

* Lint

* Resolve PR comments

* 1. type-sensitive env variable getter; 2. updated READMEs for examples

* Rl type specific env getter (#466)

* 1. type-sensitive env variable getter; 2. updated READMEs for examples

* fixed bugs

* fixed bugs

* bug fixes

* lint

Co-authored-by: ysqyang <v-yangqi@microsoft.com>
Co-authored-by: yaqiu <v-yaqiu@microsoft.com>

* Example bug fix

* Optimize parser.py

* Resolve PR comments

* added detailed doc

* lint

* wording refined

* resolved some PR comments

* rewriting rl toolkit rst

* resolved more PR comments

* typo fix

* updated rst

Co-authored-by: Huoran Li <huoranli@microsoft.com>
Co-authored-by: Default <huo53926@126.com>
Co-authored-by: ysqyang <v-yangqi@microsoft.com>
Co-authored-by: yaqiu <v-yaqiu@microsoft.com>