Clean up copy and paste code in README

[datadaveshin]

There are one-line commands in the README that have a $ prompt in them, which carry over when using the "copy" button, raising the command not found: $ message in the terminal. Minor, but thought I'd mention it and send a PR for your consideration.

Also, I thought maybe: $ RBENV_GEMSET_FILE="$HOME/hplabs/project1/.rbenv-gemsets" rails new newproject could be: RBENV_GEMSET_FILE="$HOME/<your-username>/<projects-directory>/.rbenv-gemsets" rails new <newproject> but since it's in the neckbeard section, I just removed the first $.