Update README for Cargo.toml install option

[Djboy08]

Just shows another install option for devs looking to use this in their project using Cargo.toml dependencies

[Djboy08]

Maybe add it to this page too? https://sleitnick.github.io/rbxcloud/cli/cli-install/

I also realize some pages do have the actual install method. So not sure if you are just planning on updating it later.

[jackTabsCode]

I don't see why this is necessary given the crate is published

[Sleitnick]

Gonna close this since it's not very relevant to the project