Add installation, usage, API readme

Author: aminya

README.md

@@ -1,2 +1,69 @@
 # rollup-plugin-atomic
- Rollup preset used in atom-ide-community
+
+Rollup plugin used in atom-ide-community
+
+## Installation
+
+```
+npm install --save-dev rollup-plugin-atomic
+```
+
+You should also install the peer dependencies:
+
+```
+"rollup": "2.21.0",
+```
+
+```
+"typescript": "^3.9.6",
+"coffeescript": "^1.12.7",
+"@babel/core": "^7.10.5",
+```
+
+## Usage
+
+Create a `rollup.config.js` file at the root of the project with the following content. See API section for more details
+
+```js
+const { createPlugins, createConfig } = requore("rollup-plugin-atomic");
+
+const plugins = createPlugins(["js"], true);
+
+const config = createConfig(
+  "src/x-terminal.js",
+  "dist",
+  "cjs",
+  ["atom", "electron", "node-pty-prebuilt-multiarch"],
+  plugins
+);
+
+module.exports = config;
+```
+
+## API
+
+use `createPlugins` to create the plugins you need.
+
+```ts
+createPlugins(
+  languages: Array<string> = ["ts", "js", "json", "coffee"], // languages you use
+  babel: boolean = true,     // if you want to use babel
+  extraPlugins?: Array<any>	// pass any extra plugins functions like `multientry()`
+)
+```
+
+use `createConfig` to create the configs you need
+
+```ts
+createConfig(
+  input: string | Array<string> = "src/main.ts", // bundle's input(s) file(s)
+  output_dir: string = "dist",	// where the bundle is stored
+  output_format = "cjs",  // output format (e.g. `cjs`, `es`, etc)
+  externals: Array<string> = ["atom", "electron"], // libraries you want to be external
+  plugins = createPlugins() // pass the plugins you created using `createPlugins()`
+)
+```
+You can create multiple configs using `createConfig` and export them as an array:
+```js
+module.exports = [config1, config2]
+```