Update README.md

Author: codeaholicguy

README.md

@@ -1,3 +1,62 @@
 # fastify-response-caching
 
 ![Node.js CI](https://github.com/codeaholicguy/fastify-response-caching/workflows/Node.js%20CI/badge.svg)
+
+*fastify-response-caching* is a plugin for the [Fastify](http://fastify.io/) framework 
+that provides mechanisms for caching response to reduce the server workload.
+
+By default, this plugin implements caching by request URL (includes all query parameters)
+with the caching time (TTL) is 1 seconds. Besides, this plugin also supports additional caching condition
+such as request headers.
+
+## Example
+
+This example shows using the plugin to cache response with default options.
+
+```js
+const fastify = require('fastify')
+const fastifyResponseCaching = require('fastify-response-caching')
+
+fastify.register(fastifyResponseCaching)
+```
+
+This example shows using the plugin to cache response with customized caching time.
+
+```js
+const fastify = require('fastify')
+const fastifyResponseCaching = require('fastify-response-caching')
+
+fastify.register(fastifyResponseCaching, {ttl: 5000})
+```
+
+This example shows using the plugin to cache response with customized caching conditions.
+
+```js
+const fastify = require('fastify')
+const fastifyResponseCaching = require('fastify-response-caching')
+
+fastify.register(fastifyResponseCaching, {ttl: 5000, headers: ['x-request-agent']})
+```
+
+## API
+
+### Options
+
+*fastify-response-caching* accepts the options object:
+
+```js
+{
+  ttl: <Number>
+  additionalCondition: {
+    headers: <Array<String>>
+  }
+}
+```
+
++ `ttl` (Default: `1000`): a value, in milliseconds, for the lifetime of the response cache.
++ `additionalCondition` (Default: `undefined`): a configuration of additional condition for caching.
++ `additionalCondition.headers` (Default: `[]`): a list of string, headers that you want to include in the caching condition.
+
+## License
+
+[MIT License](LICENSE)