Make code-creation docs discoverable

What does this merge request do and why?

• Link the code-creation pipeline docs into the main README
• Remove "Base Usage" section in the README which leads the user to think that one can only run Code Completion pipelines.

Fix #294 (closed)

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• I've ran the affected pipeline(s) to validate that nothing is broken.
• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.