Copy-and-paste Go client example (#4448)

* Copy-and-paste Go client example

Includes Go source that runs without modification, as well as simple
instructions for compiling, running, and viewing the output in the
Consul UI.

* Remove unnecessary flags from development server example

This is a bare minimum Go example needed to store keys and values in
Consul. The `-ui` and `-server` flags aren't needed when running with
`-dev`.

api/README.md

@@ -17,27 +17,51 @@ Usage
 Below is an example of using the Consul client:
 
 ```go
-// Get a new client
-client, err := api.NewClient(api.DefaultConfig())
-if err != nil {
-    panic(err)
+package main
+
+import "github.com/hashicorp/consul/api"
+import "fmt"
+
+func main() {
+	// Get a new client
+	client, err := api.NewClient(api.DefaultConfig())
+	if err != nil {
+		panic(err)
+	}
+
+	// Get a handle to the KV API
+	kv := client.KV()
+
+	// PUT a new KV pair
+	p := &api.KVPair{Key: "REDIS_MAXCLIENTS", Value: []byte("1000")}
+	_, err = kv.Put(p, nil)
+	if err != nil {
+		panic(err)
+	}
+
+	// Lookup the pair
+	pair, _, err := kv.Get("REDIS_MAXCLIENTS", nil)
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("KV: %v %s\n", pair.Key, pair.Value)
 }
-
-// Get a handle to the KV API
-kv := client.KV()
-
-// PUT a new KV pair
-p := &api.KVPair{Key: "foo", Value: []byte("test")}
-_, err = kv.Put(p, nil)
-if err != nil {
-    panic(err)
-}
-
-// Lookup the pair
-pair, _, err := kv.Get("foo", nil)
-if err != nil {
-    panic(err)
-}
-fmt.Printf("KV: %v", pair)
-
 ```
+
+To run this example, start a Consul server:
+
+```bash
+consul agent -dev
+```
+
+Copy the code above into a file such as `main.go`.
+
+Install and run. You'll see a key (`REDIS_MAXCLIENTS`) and value (`1000`) printed.
+
+```bash
+$ go get
+$ go run main.go
+KV: REDIS_MAXCLIENTS 1000
+```
+
+After running the code, you can also view the values in the Consul UI on your local machine at http://localhost:8500/ui/dc1/kv