Add note about running next without a sub-command (#36560)

This should be made explicitly clear because other code may just call `next` instead of `next dev` (e.g. https://github.com/netlify/framework-info/blob/main/src/frameworks/next.json).

Being in the ninth circle of debug hell right now I could not take it for granted that the two were the same till I saw some kind of confirmation, either from the docs or from the source.  Source is great, but calling it out in the docs would saved me some time.



## 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

- [ ] Make sure the linting passes by running `yarn lint`

docs/api-reference/cli.md

@@ -39,6 +39,8 @@ NODE_OPTIONS='-r esm' next
 NODE_OPTIONS='--inspect' next
 ```
 
+> Note: Running `next` without a command is the same as running `next dev`
+
 ## Build
 
 `next build` creates an optimized production build of your application. The output displays information about each route.