update bootstrap.sh for macOS brew using steps from The Book

See merge request !1231

Install cargo-config from bootstrap script

See merge request !1230

Some cookbook entries were failing with an error like this:

```
error: no such subcommand: `config`
```

We can install this subcommand from the bootstrap script, and also
instruct folks in the README to do so manually.

This reverts commit c5d3a92a.