docs: add example and correct usage of `[click]` & `[click:{n+1}]`

[gy-mate]

Documenting the behavior described at https://github.com/slidevjs/slidev/issues/1680#issuecomment-2197852296

[netlify[bot]]

❌ Deploy Preview for slidev failed.

Name	Link
🔨 Latest commit	30987e192cc5098dcd4d8dc7aed4df5a3752d2d9
🔍 Latest deploy log	https://app.netlify.com/sites/slidev/deploys/668005e6ef573d0008a4364d