docs(script): explain expected `next/script` behavior on client-side navigation (#42260)
docs(script): explain expected `next/script` behavior on client-side navigation (#42260)

This PR explains that a navigation via `Link` would not re-execute
`next/script` components once they are added.

Fixes #42111

Ref: [slack
thread](https://vercel.slack.com/archives/C02UJ0QH45Q/p1667237775929339)

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

Co-authored-by: JJ Kasper <7323a5431d1c31072983a6a5bf23745b655ddf59@jjsweb.site>
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