docs: update get-static-paths.md (#40205)
docs: update get-static-paths.md (#40205)

I found that `fallback: true` behaves like `fallback: blocking` when client-side page transition, but document doesn't mention the behavior.
I tried following.

* created a SSG page which has getStaticPaths and getStaticProps, and the getStaticProps is too slow(something like `await setTimeout(10000)`)
* `next build && next start`, not `next dev`
* tried page reload and client-side page transition both

getServerSideProps document explains about client-side page transition.
https://nextjs.org/docs/basic-features/data-fetching/get-server-side-props#when-does-getserversideprops-run

On the other hand, getStaticPaths didn't explain this behavior, so I added it.



## Bug

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

## Documentation / Examples

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

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