Augment bitwise.sand() function and example explanation

User feedback on adding more info about the bitwise.sand() function.

" tells me nothing about the function or its purpose. the example should be explained why 4 is the result. the example does not work"

https://docs.influxdata.com/flux/v0.x/stdlib/experimental/bitwise/sand/

Open the linked bitwise.sand() documentation page and review its function description and example. Verify why the example should produce 4 and whether it runs as shown; done means the page explains the function's purpose and includes a working, understandable example.

Written by the indexing model from the issue text.