update create-next-app documentation (vercel#25079)

Update `create-next-app` documentation based in vercel#25010 issue. 


## Documentation / Examples

- [X] Make sure the linting passes

Author: arroiz

docs/api-reference/create-next-app.md

@@ -18,7 +18,7 @@ yarn create next-app
 
 - **-e, --example [name]|[github-url]** - An example to bootstrap the app with. You can use an example name from the [Next.js repo](https://github.com/vercel/next.js/tree/master/examples) or a GitHub URL. The URL can use any branch and/or subdirectory.
 - **--example-path [path-to-example]** - In a rare case, your GitHub URL might contain a branch name with a slash (e.g. bug/fix-1) and the path to the example (e.g. foo/bar). In this case, you must specify the path to the example separately: `--example-path foo/bar`
-- **--use-npm** - Explicitly tell the CLI to bootstrap the app using npm. Yarn will be used by default if it's installed
+- **--use-npm** - Explicitly tell the CLI to bootstrap the app using npm. To bootstrap using yarn we recommend to run `yarn create next-app`
 
 ### Why use Create Next App?
 

packages/create-next-app/README.md

@@ -19,7 +19,7 @@ npx create-next-app blog-app
 - **--ts, --typescript** - Initialize as a TypeScript project.
 - **-e, --example [name]|[github-url]** - An example to bootstrap the app with. You can use an example name from the [Next.js repo](https://github.com/vercel/next.js/tree/master/examples) or a GitHub URL. The URL can use any branch and/or subdirectory.
 - **--example-path <path-to-example>** - In a rare case, your GitHub URL might contain a branch name with a slash (e.g. bug/fix-1) and the path to the example (e.g. foo/bar). In this case, you must specify the path to the example separately: `--example-path foo/bar`
-- **--use-npm** - Explicitly tell the CLI to bootstrap the app using npm. Yarn will be used by default if it's installed
+- **--use-npm** - Explicitly tell the CLI to bootstrap the app using npm. To bootstrap using yarn we recommend to run `yarn create next-app`
 
 ## Why use Create Next App?