Docs for Frame Benchmarking (#7121)

* remove test benchmark pallet

* docs

* finish docs

* Update README.md

* simplify intro

* introduce weight later

* Apply suggestions from code review

Co-authored-by: David <[email protected]>
Co-authored-by: joe petrowski <[email protected]>
Co-authored-by: Kian Paimani <[email protected]>

* Apply suggestions from code review

Co-authored-by: David <[email protected]>
Co-authored-by: joe petrowski <[email protected]>

* Apply suggestions from code review

Co-authored-by: joe petrowski <[email protected]>
Co-authored-by: David <[email protected]>

* Apply suggestions from code review

Co-authored-by: David <[email protected]>
Co-authored-by: joe petrowski <[email protected]>

* Update frame/benchmarking/README.md

Co-authored-by: David <[email protected]>

* Update frame/benchmarking/README.md

* Update frame/benchmarking/README.md

Co-authored-by: joe petrowski <[email protected]>

* Update README.md

* Update README.md

* Update README.md

* Update README.md

Co-authored-by: David <[email protected]>
Co-authored-by: joe petrowski <[email protected]>
Co-authored-by: Kian Paimani <[email protected]>