Include --output in the docs

[kiliw]

Hello all together,

we are using your truffle-flattener and so far it works great. We saw in the code that there is the --output option to suppress the yarn comments in the flattend .sol files.

Maybe you guys can include this option in your docs? Would be better I think if one can directly get this from the README :)

Thank your very much.
Best regards.

[PfanP]

Is this package maintained?

[alcuadrado]

Closing to clean up the repository. If this problem persists, please open a new issue with a clear explanation.