prevent both npm and yarn commands from being copied (#11757)

Author: mubarakn

docusaurus/docs/adding-typescript.md

@@ -13,9 +13,9 @@ To start a new Create React App project with [TypeScript](https://www.typescript
 
 ```sh
 npx create-react-app my-app --template typescript
-
-# or
-
+```
+or
+```sh
 yarn create react-app my-app --template typescript
 ```
 
@@ -27,9 +27,9 @@ To add [TypeScript](https://www.typescriptlang.org/) to an existing Create React
 
 ```sh
 npm install --save typescript @types/node @types/react @types/react-dom @types/jest
-
-# or
-
+```
+or
+```sh
 yarn add typescript @types/node @types/react @types/react-dom @types/jest
 ```