Add inspectable attribute to guide
This was missed in PR
- [`start`](./reference/attributes/on-rust-exports/start.md)
- [`typescript_custom_section`](./reference/attributes/on-rust-exports/typescript_custom_section.md)
- [`getter` and `setter`](./reference/attributes/on-rust-exports/getter-and-setter.md)
+ - [`inspectable`](./reference/attributes/on-rust-exports/inspectable.md)
- [`web-sys`](./web-sys/index.md)
- [Using `web-sys`](./web-sys/using-web-sys.md)
