Update what-is-codegen.md (facebook#4300)

Author: alexis-salnikoff-wmx

docs/the-new-architecture/what-is-codegen.md

@@ -10,6 +10,6 @@ React Native invokes **Codegen** automatically every time an iOS or Android app
 
 **Codegen** is a process that is tightly coupled with a React Native app. The **Codegen** scripts live inside the `react-native` NPM package and the apps calls those scripts at build time.
 
-**Codegen** crawls the folders in your project, starting form a directory you specify in your `package.json`, looking for some specific JS files that contains the specification (or specs) for your custom modules and components. Spec files are JS files written in a typed dialect: React Native currently supports Flow and TypeScript.
+**Codegen** crawls the folders in your project, starting from a directory you specify in your `package.json`, looking for some specific JS files that contains the specification (or specs) for your custom modules and components. Spec files are JS files written in a typed dialect: React Native currently supports Flow and TypeScript.
 
 Every time **Codegen** finds a spec files, it generates the boilerplate code associated to it. **Codegen** generates some C++ glue-code and then it generates platform-specific code, using Java for Android and Objective-C++ for iOS.