Data 1688 setu bav decription (#197)

* add api reference for setu-bav

* add description to api setu-bav api reference

* show penny-less merchant type as example

* Add descriptions

* Fic typo

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Co-authored-by: rahul roy <rahul@setu.co>
Co-authored-by: Aditya Gannavarapu <adityagannavarapu.67@gmail.com>

Author: 3 people