fix: improve readme

README.md

@@ -1,6 +1,6 @@
 # json-reporter
 
-[![npm](https://img.shields.io/npm/v/json-reporter.svg?maxAge=2592000)](https://www.npmjs.com/package/json-reporter)
+[![npm](https://img.shields.io/npm/v/json-reporter.svg)](https://www.npmjs.com/package/json-reporter)
 [![Build Status](https://travis-ci.org/gemini-testing/json-reporter.svg?branch=master)](https://travis-ci.org/gemini-testing/json-reporter)
 [![Coverage Status](https://img.shields.io/coveralls/gemini-testing/json-reporter.svg?style=flat)](https://coveralls.io/r/gemini-testing/json-reporter?branch=master)
 
@@ -19,3 +19,64 @@ and hermione plugins [here](https://github.com/gemini-testing/hermione#plugins).
 ```bash
 npm install json-reporter
 ```
+
+## Usage
+
+Plugin has following configuration:
+
+* **enabled** (optional) `Boolean` – enable/disable the plugin; by default plugin is enabled
+* **path** (optional) `String` - path for saving json report file; by default json report will be saved into `json-reporter.json` inside current work directory.
+
+Also there is ability to override plugin parameters by CLI options or environment variables
+(see [configparser](https://github.com/gemini-testing/configparser)).
+
+### Gemini usage
+
+Add plugin to your `gemini` config file:
+
+```js
+module.exports = {
+    // ...
+    plugins: {
+        'json-reporter/gemini': {
+            enabled: true,
+            path: 'my/custom/report.json'
+        }
+    },
+    //...
+}
+```
+
+### Hermione usage
+
+Add plugin to your `hermione` config file:
+
+```js
+module.exports = {
+    // ...
+    plugins: {
+        'json-reporter/hermione': {
+            enabled: true,
+            path: 'my/custom/report.json'
+        }
+    },
+    //...
+}
+```
+
+## Testing
+
+Run [mocha](http://mochajs.org) tests:
+```bash
+npm run test-unit
+```
+
+Run tests with [istanbul](https://github.com/gotwarlost/istanbul) coverage calculation:
+```bash
+npm run cover
+```
+
+Run [eslint](http://eslint.org) codestyle verification
+```bash
+npm run lint
+```