Update README

Author: fatfisz

README.md

@@ -1,19 +1,32 @@
 # eslint-config-codility
+
 Codility's shared ESLint config.
 
 ## Usage
-1. Install the package: `yarn add @codility/eslint-config-codility -D -E`
-2. Install peer dependencies
+
+1. Install the package: `yarn add @codility/eslint-config-codility --dev --exact`
+2. Install peer dependencies and optional dependencies if needed
 3. Add `.eslintrc.js` file:
-```
-/* eslint-disable strict */
+  * For the vanilla JS version use this:
+    ```
+  /* eslint-disable strict */
 
-'use strict';
+  'use strict';
 
-module.exports = {
-  extends: ['@codility/eslint-config-codility'],
-};
-```
+  module.exports = {
+      extends: ['@codility/eslint-config-codility'],
+  };
+  ```
+  * For the React version use this:
+    ```
+  /* eslint-disable strict */
+
+  'use strict';
+
+  module.exports = {
+      extends: ['@codility/eslint-config-codility/react'],
+  };
+  ```
 4. Add `scripts` to your `package.json`:
 ```
 "lint": "eslint .",
@@ -22,6 +35,10 @@ module.exports = {
 5. Run lint with `yarn lint`
 6. Let the tool fix your code: `yarn lint:fix`
 
+## Migrating to v.2
+
+Previously the only version available included React plugins and had React as a peer dependency, which was annoying for projects that didn't involve it. That version is now available as `@codility/eslint-config-codility/react` - simply add `/react` at the end.
+
 ## Warnings vs errors rationale
 
 Rules for setting up the rules:
@@ -30,7 +47,7 @@ Rules for setting up the rules:
   - we don't care about the rule
   - we really don't
 - 1 (warn):
-  - the code can run, but we don't want it on production
+  - the code can run, but we don't want it on production (e.g. `console.log` or `debugger`)
   - stylistic errors
 - 2 (error):
   - the code can't run