Document code sending features and vim slime dependency

[taprati]

Hello, thank you for all the great work you're doing! Enjoying using the package so far. I wanted to use the various QuartoSend functions you have implemented, and I was able to get it to work, but it might be useful to document vim slime as a dependency / explain how to set that up. I was able to discern through error messages and some of the code in your kickstarter config, but might be clearer to include as info in the package.