Merge pull request #40 from ruflin/readme

Add basic README docs

README.md

@@ -1,8 +1,84 @@
-# ucfg
-
 [![Build
 Status](https://travis-ci.org/elastic/go-ucfg.svg?branch=master)](https://travis-ci.org/elastic/go-ucfg)
-
 [![Go Report
 Card](https://goreportcard.com/badge/github.com/elastic/go-ucfg)](https://goreportcard.com/report/github.com/elastic/go-ucfg)
 
+
+# ucfg - Universal Configuration
+
+`ucfg` is a Golang library to handle yaml and json configuration files in your Golang project. It was developed for the [libbeat framework](https://github.com/elastic/beats/tree/master/libbeat) and used by all [beats](https://github.com/elastic/beats).
+
+
+## API Documentation
+
+The full API Documentat can be found [here](https://godoc.org/github.com/elastic/go-ucfg).
+
+## Examples
+
+A few examples on how ucfg can be used. All examples below assume, that the following packages are imported:
+
+```
+import (
+	"github.com/elastic/go-ucfg"
+	"github.com/elastic/go-ucfg/yaml"
+)
+```
+
+
+### Dot notations
+
+ufcg allows you to load yaml configuration files using dots instead of indentation. For example instead of having:
+
+```
+config:
+  user: name
+```
+
+with ucfg you can write:
+
+```
+config.user: name
+```
+
+This makes configurations easier and simpler.
+
+To load such a config file in Golang, use the following command:
+
+```
+config, err := yaml.NewConfigWithFile(path, ucfg.PathSep("."))
+```
+
+
+
+### Validation and Defaults
+
+ucfg allows to automatically validate fields and set defaults for fields in case they are not defined.
+
+
+```
+// Defines struct to read config from
+type ExampleConfig struct {
+    Counter  string 	`config:"username" validate:"min=0, max=9"`
+}
+
+// Defines default config option
+var (
+    defaultConfig = ExampleConfig{
+		    Counter: 4,
+    }
+}
+
+func main() {
+    config, err := yaml.NewConfigWithFile(path, ucfg.PathSep("."))
+    config.Unpack(defaultConfig)
+}
+```
+
+The above uses `Counter` as the config variable. ucfg assures that the value is between 0 and 9 and will return an error if this is not the case. In addition, if the value is not set, it will default to 4.
+
+
+## Requirements
+
+ucfg has the following requirements:
+
+* Golang 1.6