Typo in non-rustup-setups.md

[dallasbrittany]

🐛 Bug description

In the Non-rust setups section of the Prerequisites section (docs/src/prerequisites/non-rustup-setups.md), it's missing a word and could use a few other minor improvements.
Current text:
"However, if you're not using Rustup we won't be able to this automatically and you'll have to do this yourself."

🤔 Expected Behavior

The text should probably be this:
"However, if you're not using Rustup, then we won't be able to do this automatically, and you'll have to do this yourself."