Vanity URL for the installer

Made with
`https://github.com/bbatsov/prelude/raw/master/utils/installer.sh`

More info: https://github.com/bbatsov/prelude/raw/master/utils/installer.sh
Use valid shell commands

By not prepending `$` to your examples users can copy them easier
without fear of seeing `bash: $: command not found` or similar
Merge pull request #333 from joshuarh/vanity-url

Vanity URL for the installer
Merge pull request #334 from joshuarh/valid-shell-commands

Valid shell commands