update example in readme (#150)

README.md

@@ -26,27 +26,37 @@ Library Example usage:
 package main
 
 import (
+    "context"
     "fmt"
     "time"
+
     goipam "github.com/metal-stack/go-ipam"
 )
 
 func main() {
-    // create a ipamer with in memory storage
-    ipam := goipam.New()
-
-
+    // The background context
     bgCtx := context.Background()
-    // Optional with Namespace
-    ctx := goipam.NewContextWithNamespace(bgCtx, "tenant-a")
 
+    // Create a ipamer with in memory storage
+    ipam := goipam.New(bgCtx)
+
+    // Optionally, we can pass around a context for a given namespace
+    namespace := "tenant-a"
+    err := ipam.CreateNamespace(bgCtx, namespace)
+    if err != nil {
+        panic(err)
+    }
+    ctx := goipam.NewContextWithNamespace(bgCtx, namespace)
     ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
     defer cancel()
+
+    // Create a prefix to manage some IPs
     prefix, err := ipam.NewPrefix(ctx, "192.168.0.0/24")
     if err != nil {
         panic(err)
     }
 
+    // Acquire and release an IP with this prefix
     ip, err := ipam.AcquireIP(ctx, prefix.Cidr)
     if err != nil {
         panic(err)
@@ -64,11 +74,13 @@ func main() {
     if err != nil {
         panic(err)
     }
+
     cp1, err := ipam.AcquireChildPrefix(ctx, prefix.Cidr, 64)
     if err != nil {
         panic(err)
     }
     fmt.Printf("got Prefix: %s\n", cp1)
+
     cp2, err := ipam.AcquireChildPrefix(ctx, prefix.Cidr, 72)
     if err != nil {
         panic(err)