Add folder structure docs for new contributors (facebook#1991)

* Adding folder structure to help people navigate through project. It helps in resolving issues by providing brief description of each package and its purpose

* Removing unnecessary packages from Folder structure heading

* Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -41,6 +41,36 @@ Please **ask first** if somebody else is already working on this or the core dev
 
 Please also provide a **test plan**, i.e. specify how you verified that your addition works.
 
+## Folder Structure of Create React App
+`create-react-app` is a monorepo, meaning it is divided into independent sub-packages.<br>
+These packages can be found in the [`packages/`](https://github.com/facebookincubator/create-react-app/tree/master/packages) directory.
+
+### Overview of directory structure
+```
+packages/
+  babel-preset-react-app/
+  create-react-app/
+  eslint-config-react-app/
+  react-dev-utils/
+  react-scripts/
+```
+### Package Descriptions
+#### [babel-preset-react-app](https://github.com/facebookincubator/create-react-app/tree/master/packages/babel-preset-react-app)
+This package is a babel preset intended to be used with `react-scripts`.<br>
+It targets platforms that React is designed to support (IE 9+) and enables experimental features used heavily at Facebook.<br>
+This package is enabled by default for all `create-react-app` scaffolded applications.
+#### [create-react-app](https://github.com/facebookincubator/create-react-app/tree/master/packages/create-react-app)
+The global CLI command code can be found in this directory, and shouldn't often be changed. It should run on Node 0.10+.
+#### [eslint-config-react-app](https://github.com/facebookincubator/create-react-app/tree/master/packages/eslint-config-react-app)
+This package contains a conservative set of rules focused on making errors apparent and enforces no style rules.<br>
+This package is enabled by default for all `create-react-app` scaffolded applications.
+#### [react-dev-utils](https://github.com/facebookincubator/create-react-app/tree/master/packages/react-dev-utils)
+This package contains utilities used for `react-scripts` and sister packages.<br>
+Its main purpose is to conceal code which the user shouldn't be burdened with upon ejecting.
+#### [react-scripts](https://github.com/facebookincubator/create-react-app/tree/master/packages/react-scripts)
+This package is the heart of the project, which contains the scripts for setting up the development server, building production builds, configuring all software used, etc.<br>
+All functionality must be retained (and configuration given to the user) if they choose to eject.
+
 ## Setting Up a Local Copy
 
 1. Clone the repo with `git clone https://github.com/facebookincubator/create-react-app`