Adding ##Motivation section to documentation.

[liangXD523]

Description

Adding ##Motivation section to update the documentation on the website.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Documentation only change (no code changed)

Screenshots

Please attach before and after screenshots of the change if applicable.

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files
• I have run ruff check . and ruff format
• I have run mypy .
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[liangXD523]

Let me deal with ruff and push the changes.

[liangXD523]

Let me deal with ruff and push the changes.

It’s done. Please take a look, as I can’t preview how the math equations will render on the website. I assume the documentation changes will show up once this PR is merged and the main branch is updated?