Update README (#20)

README.md

@@ -1,5 +1,87 @@
 # Grafana RRD Server
 
-[![CircleCI](https://circleci.com/gh/doublemarket/grafana-rrd-server/tree/master.svg?style=svg)](https://circleci.com/gh/doublemarket/grafana-rrd-server/tree/master)
+A simple HTTP server that reads RRD files and responds to requests from Grafana with [Grafana Simple JSON Datasource plugin](https://grafana.net/plugins/grafana-simple-json-datasource).
 
-A simple HTTP server that reads RRD files and responds to requests from Grafana with [Grafana Simple JSON Datastore plugin](https://grafana.net/plugins/grafana-simple-json-datasource).
+[![CircleCI](https://img.shields.io/circleci/project/github/doublemarket/grafana-rrd-server.svg)](https://github.com/doublemarket/grafana-rrd-server)
+[![GitHub release](https://img.shields.io/github/release/doublemarket/grafana-rrd-server.svg)](https://github.com/doublemarket/grafana-rrd-server/releases)
+
+# Requirement
+
+- librrd-dev (rrdtool)
+- Go
+- Grafana 3.0 and newer + Simple JSON Datasource plugin 1.0.0 and newer
+
+# Usage
+
+1. Install librrd-dev (rrdtool).
+
+   On Ubuntu/Debian:
+
+   ```
+   sudo apt install librrd-dev
+   ```
+
+   On CentOS:
+
+   ```
+   sudo yum install rrdtool-devel
+   ```
+
+   On Mac:
+
+   ```
+   brew install rrdtool
+   ```
+
+2. Get the package.
+
+   ```
+   go get github.com/doublemarket/grafana-rrd-server
+   ```
+
+   Otherwise, download [the latest release](https://github.com/doublemarket/grafana-rrd-server/releases/latest), gunzip it, and put the file in a directory included in `$PATH`:
+
+   ```
+   gunzip grafana-rrd-server_linux_amd64.gz
+   ```
+
+3. Run the server.
+
+   ```
+   grafana-rrd-server
+   ```
+
+   You can use the following options:
+
+   - `-h` : Shows help messages.
+   - `-p` : Specifies server port. (default: 9000)
+   - `-r` : Specifies a directory path keeping RRD files. (default: "./sample/")
+     - The server recursively searches RRD files under the directory and returns a list of them for the `/search` endpoint.
+   - `-s` : Default graph step in second. (default: 10)
+     - You can see the step for your RRD file using:
+       ```
+       $ rrdtool info [rrd file] | grep step
+       step = 300
+       ```
+
+4. Setup Grafana and Simple JSON Datastore plugin.
+
+   See [Grafana documentation](http://docs.grafana.org/)
+
+5. Create datasource.
+
+# Contributing
+
+1. Install librrd-dev (rrdtool).
+
+   See the Usage section.
+
+2. Clone the repository.
+
+3. Commit your code on a separate branch.
+
+4. Create a pull request.
+
+# License
+
+MIT