Markdown rendering for mermaid diagrams and notes

[albinsuresh]

Proposed changes

This PR includes two markdown rendering improvements:

1. Render mermaid diagrams using https://github.com/badboy/mdbook-mermaid
2. Render admonish blocks for note, warning and example blocks using https://tommilligan.github.io/mdbook-admonish/

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

#1661

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s)
• I ran cargo fmt as mentioned in CODING_GUIDELINES
• I used cargo clippy as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[didier-wenzek]

I would be good to update the README to install all the mdbook add-ons.

cargo install mdbook mdbook-linkcheck mdbook-mermaid mdbook-admonish

There is also a warning on mdbook build: The command wasn't found, is the "admonish" preprocessor installed?. One needs to update the files gh-pages.yml and pull-request-check.yaml.

[didier-wenzek]

Approved