[#23] Update README.md for more clarity in building requests

[seanaye]

Issue

Fixes #23

Details

PR adds and extra example of post request in readme and comments about how to find docs for custom requests

CheckList

• [x] PR starts with [#_ISSUEID].
• [x] Has been tested (where required) before merge to main.

[asos-craigmorten]

Nice - thanks @seanaye