["Request"] mention result computation block API in learning docs

[postfixNotation]

The either, nullable and option computation block APIs have all been covered in the learning docs. But if you are gradually integrating Arrow's APIs into your project, chances are you are using the Result API from Kotin's standard lib.

Therefore it might be very beneficial to add the result API to aforementioned documentation, since otherwise it's very unlikely that it will be found by newcomers and even experienced Arrow users. As discussed with @nomisRev it should probably go here (source).