Ideally, we should add:

• a description and examples of how to call compute functions
• an API reference for concrete C++ functions such as Cast, NthToIndices, etc.

Reporter: Antoine Pitrou / @pitrou

Related issues:

• [C++] Document available functions in compute::FunctionRegistry (depends upon)

_{Note: This issue was originally created as ARROW-9392. Please see the migration documentation for further details.}