fix/docs(readme): javascript truthy shenanigans

[joachimbulow]

This specific section is confusing.

indexOf returns -1 when the string is not found, i.e. a truthy value.
Hence, the docs suggest that for some reason, the napMap application would apply if and only if the index of the string 30001 is not 0.

I think it would be a clearer read to use includes as it more accurately aligns with an expected usecase