Documentation for shellcheck should include that it is configurable with a .shellcheckrc

**Describe the solution you'd like**
A simple `README.md` update is needed to clarify that in addition to the `--enable` flag, the `.shellcheckrc` can be used to configure additional entries.

**Describe alternatives you've considered**
Linking directly to the `shellcheck` documentation

**Additional context**
Allow for passing cli args directly through to `shellcheck`

> Other shellcheck flags can not be passed through.

Which is true, but is misleading to those looking for an option to set `disable` entries.