README.md: Add documentation about 32bit values

[marcosps]

Using an array when calling methods from jsmodbus implies that all values are in fact 16bit, so exemplify how to use jsmodbus with 32bit values.

Signed-off-by: Marcos Paulo de Souza marcos.souza.org@gmail.com

[marcosps]

Added some documentation about this matter, as I suffered trying to grasp how to do it.

Please let me know if you want me to change anything.

Thanks,

[stefanpoeter]

Thanks a lot.