chore: update generate comment

[jackchuka]

This pull request enhances the schema and code generation for documentation sections by introducing support for section descriptions, improving code block placeholder comments based on language, and refining structural guidance. The main changes are grouped below.

Schema and Documentation Generation Improvements:

• Added a Description field to the StructureElement struct in schema.go, allowing schema authors to provide section descriptions that are output as HTML comments in generated documentation (StructureElement struct, JSON schema, and schema.json). [1] [2] [3]
• Updated the generateElement function to insert the section description as an HTML comment if present.

Code Block Generation Enhancements:

• Introduced the commentForLang helper function to generate appropriate "TODO" comments for code blocks based on their language, and updated code block generation to use this function for more contextually correct placeholder comments. [1] [2]

Structural Guidance Refinements:

• Removed the "Required section" comment from structural content generation and associated tests, focusing instead on providing ordering guidance for child sections. [1] [2]