Add keyword "distributed" to QRack's description

[WingCode]

I think it would be worthwhile to mention the keyword distributed in the Qrack's description. I could find the word "distributed" in their README.md

For people looking out from distributed quantum computing simulator framework under the UnitaryFund projects page this would be helpful. Going into each simulator's repo and looking whether it is distributed takes more effort. Maybe this will also help Google to index QRack with keywords "distributed", "quantum simulator" keywords even better.

[willzeng]

@WrathfulSpatula what do you think? Want to make the update?

[WrathfulSpatula]

Thank you again, @WingCode! It sounds like you're having success beyond my proof-of-concept work in distributed simulation with Qrack, but this all sounds good to me!