Update README.md

[cohms]

This is a:

• [ x] documentation update

Description & motivation

Added example on the right syntax for using multiple arguments to generate_source in the Cloud IDE

Without this it wasn't clear how to call multiple arguments in the Cloud IDE. I've had customers try copying the macro syntax shown which doesn't work ( e.g. try 'schema_name': 'jaffle_shop',... instead of schema_name= 'jaffle_shop',...)

Checklist

• [ ] This code is associated with an issue which has been triaged and accepted for development.
• [x] I have verified that these changes work locally
• [x] I have updated the README.md (if applicable)
• [ ] I have added tests & descriptions to my models (and macros if applicable)
• [ ] I have added an entry to CHANGELOG.md

[graciegoheen]

Yep - let's open up a new issue to resolve CI checks, but we can go ahead and merge this