Adding mermaidJS for mermaid graphs

[ImtiazKhanDS]

name: Pull Request for adding Mermaid Graphs

about: Propose changes to the codebase title: 'Add Mermaid graphs in fasthtml websites.' labels: 'graphs' assignees: 'Jeremy'

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Related Issue Please link to the issue that this pull request addresses. If there isn't one, please create an issue first.

Proposed Changes Describe the big picture of your changes here. If it fixes a bug or resolves a feature request, be sure to link to that issue.

Types of changes What types of changes does your code introduce? Put an x in all the boxes that apply:

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist Go over all the following points, and put an x in all the boxes that apply:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.
• [x] I am aware that this is an nbdev project, and I have edited, cleaned, and synced the source notebooks instead of editing .py or .md files directly.

Additional Information Any additional information, configuration or data that might be necessary to reproduce the issue.