docs: show README content on docs.rs

[jonathanhefner]

Use #![doc = include_str!("../README.md")] to display README as crate documentation on docs.rs for both rmcp and rmcp-macros.

Changes to support this:

• Fix code examples to compile as doc tests (rust,no_run)
• Fix broken rustdoc links with explicit crate:: paths
• Add "Structured Output" section and examples link to rmcp README
• Simplify rmcp-macros README to a summary table with doc links
• Fix grammar throughout
• Add CSS to hide GitHub badges when rendered as rustdoc

🤖 Generated with Claude Code

Tip

To add new guide documentation in the future, create markdown files in a docs/ subdirectory and include them as doc modules in lib.rs:

#[doc = include_str!("../docs/guide-name.md")]
pub mod _guide_name {}

This creates navigable sections in docs.rs while keeping files maintainable.