Add usage example to README

README.md

@@ -5,3 +5,55 @@
 ```Go
 import "github.com/kelseyhightower/envconfig"
 ```
+
+## Usage
+
+Set some environment variables:
+
+```Bash
+export MYAPP_DEBUG=false
+export MYAPP_PORT=8080
+export MYAPP_USER=Kelsey
+export MYAPP_RATE="0.5"
+```
+
+Write some code:
+
+```Go
+package main
+
+import (
+    "fmt"
+    "log"
+
+    "github.com/kelseyhightower/envconfig"
+)
+
+type Specification struct {
+    Debug bool
+    Port  int
+    User  string
+    Rate  float32
+}
+
+func main() {
+    var s Specification
+    err := envconfig.Process("myapp", &s)
+    if err != nil {
+        log.Fatal(err.Error())
+    }
+    _, err = fmt.Printf("Debug: %v\nPort: %d\nUser: %s\nRate: %f\n", s.Debug, s.Port, s.User, s.Rate)
+    if err != nil {
+        log.Fatal(err.Error())
+    }
+}
+```
+
+Results:
+
+```Bash
+Debug: false
+Port: 8080
+User: Kelsey
+Rate: 0.500000
+```