docs: add how it works

Author: oklas

docs/how-it-works.md

@@ -0,0 +1,18 @@
+# How it works
+
+The library `create-react-app` is an executable that generates minimal simple apps with
+`react-scripts` dependency. The `react-scripts` is a complicated library that has webpack
+and jest and other configuration files. It makes app simple by doing all the complicated
+work it configures webpack with plugins and loaders, configure jest, etc.
+
+If someone wants to modify configuration, react-scripts suggests eject command.
+Eject copys all mentioned config files to your project so you can modify it.
+But after eject the project owner must update and fix configuration which requires
+knowledge and attention to packages updates and security fixes. Updating `react-sctipt`
+is more simple but it is not possible after eject.
+
+The library `react-scripts` does not provide a way to get runtime configs and do some
+fixes. There are some libraries like `react-app-rewired`, `customize-cra`, `craco` that do
+runtime patch configs of `react-scripts` and pass final config to user function to modify.
+
+The react-app-alias library confgures aliases in runtime.