doc-fix: heading hierarchy for Forward Operators section

[hkershaw-brown]

Description:

Added a ===== to the top level heading so only the top level appears in the table of contents.

Fixes issue

fixes #797

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Documentation changes needed?

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.

Tests

Please describe any tests you ran to verify your changes.

Here is the doc build before:

Here is the doc build after:

"Approaches for Common Situations" and "Parallelism Implementation Details" are now subsections:

Checklist for merging

• Updated changelog entry
• Documentation updated
• Update conf.py

Checklist for release

• Merge into main
• Create release from the main branch with appropriate tag
• Delete feature-branch

Testing Datasets

• Dataset needed for testing available upon request
• Dataset download instructions included
• No dataset needed