Add package-runner note to readme (#8132)

* Add package-runner note to readme

* Add link to `yarn create`

README.md

@@ -16,6 +16,7 @@ npx create-react-app my-app
 cd my-app
 npm start
 ```
+If you've previously installed `create-react-app` globally via `npm install -g create-react-app`, we recommend you uninstall the package using `npm uninstall -g create-react-app` to ensure that npx always uses the latest version.
 
 _([npx](https://medium.com/@maybekatz/introducing-npx-an-npm-package-runner-55f7d4bd282b) comes with npm 5.2+ and higher, see [instructions for older npm versions](https://gist.github.com/gaearon/4064d3c23a77c74a3614c498a8bb1c5f))_
 
@@ -61,7 +62,7 @@ _`npm init <initializer>` is available in npm 6+_
 yarn create react-app my-app
 ```
 
-_`yarn create` is available in Yarn 0.25+_
+_[`yarn create <starter-kit-package>`](https://yarnpkg.com/lang/en/docs/cli/create/) is available in Yarn 0.25+_
 
 It will create a directory called `my-app` inside the current folder.<br>
 Inside that directory, it will generate the initial project structure and install the transitive dependencies: