Document how to use TypeScript with Babel

[Kocal]

Just a reminder to write a documentation for using TypeScript with Babel (and not with ts-loader).

See those links for more info:

• https://iamturns.com/typescript-babel/
• https://github.com/microsoft/TypeScript-Babel-Starter
• https://devblogs.microsoft.com/typescript/typescript-and-babel-7/

[Kocal]

Closing since #694 has been merged.
I will work on a PR on symfony-docs