added postcss hello world app

[ProgrammingFire]

By making a PR you are agreeing to that contributing a hello world project allows the repo/project owner to use the hello world app in examples for their own use.

• [x] only the most simple basic hello world app
• [x] no styling
• [x] remove all tests and commands for tests and dependencies for tests
• [x] must say "Hello World" on the main component
• [x] only include the minimal components (1 ideally)
• [x] no routing, not extras whatsoever
• [x] nothing else !
• [x] must work by running npm install and npm start (or equivalent)
• [x] must be in the folder named <tech-name>
• [x] add build steps and which folder to serve in the README.md in the root folder
• [x] verify that the app once built can be served from whatever folder the built assets are placed in
• [x] verify that running npx http-server <your-folder-to-serve> works
• [x] verify that a Pull Request doesn't already exist. If it does, feel free to contribute to it.