docs: advise users of create-next-app --ts, --typescript (vercel#25349

)

Since vercel#24655 landed in 10.2.1, I wanted to update the documentation, especially for the top Google results for "next typescript", so that users know how to create a TS project.

Please feel free to change anything you feel is appropriate.

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

@@ -12,10 +12,19 @@ npx create-next-app
 yarn create next-app
 ```
 
+You can create a [TypeScript project](https://github.com/vercel/next.js/blob/canary/docs/basic-features/typescript.md) with the `--ts, --typescript` flag:
+
+```bash
+npx create-next-app --ts
+# or
+yarn create next-app --typescript
+```
+
 ### Options
 
 `create-next-app` comes with the following options:
 
+- **--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. To bootstrap using yarn we recommend to run `yarn create next-app`

docs/basic-features/typescript.md

@@ -11,9 +11,23 @@ description: Next.js supports TypeScript by default and has built-in types for p
   </ul>
 </details>
 
-Next.js provides an integrated [TypeScript](https://www.typescriptlang.org/) experience out of the box, similar to an IDE.
+Next.js provides an integrated [TypeScript](https://www.typescriptlang.org/)
+experience out of the box, similar to an IDE.
 
-To get started, create an empty `tsconfig.json` file in the root of your project:
+## `create-next-app` support
+
+You can create a TypeScript project with [`create-next-app`](https://nextjs.org/docs/api-reference/create-next-app) using the `--ts, --typescript` flag like so:
+
+```
+npx create-next-app --ts
+# or
+yarn create next-app --typescript
+```
+
+## Existing projects
+
+To get started in an existing project, create an empty `tsconfig.json` file in
+the root folder:
 
 ```bash
 touch tsconfig.json

packages/create-next-app/README.md

@@ -6,6 +6,12 @@ The easiest way to get started with Next.js is by using `create-next-app`. This
 npx create-next-app
 ```
 
+Or, for a [TypeScript project](https://github.com/vercel/next.js/blob/canary/docs/basic-features/typescript.md):
+
+```bash
+npx create-next-app --typescript
+```
+
 To create a new app in a specific folder, you can send a name as an argument. For example, the following command will create a new Next.js app called `blog-app` in a folder with the same name:
 
 ```bash