How to add Typescript to existing ReactJS project? Step-by-step tutorial

[Git repository in the description]
Did you create a new ReactJS project with no Typescript support?
In this video on existing project I will show you how to add Typescript to your project.

00:00 - Facebook docs "Adding Typescript"
00:35 - Installing types
02:00 - Changing .js files to .tsx

[danielshijakovski]

Question, can I at least start the migration by only making NEW component files as .tsx and keep the existing files as .js?
Then in the future maybe incrementally update the old files from .js to .tsx