doc: add the example of training on QA env with/without tool

[cameron-chen]

TODO:

• Add example command for training on QA env with/without tool
• Add the reminder for installing the additional deps in the search tool example: this will be done after the main README is set up.

[cameron-chen]

@lkevinzc would it be fine to put a script for starting the local retrieval server in examples\?

[lkevinzc]

LGTM! Feel free to squash and merge when it's ready!