rpc: update client documentation

Add missing methods, move example into something that can be compiled (and fix
it along the way).

pkg/rpc/client/doc_test.go

@@ -0,0 +1,33 @@
+package client_test
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"github.com/nspcc-dev/neo-go/pkg/rpc/client"
+)
+
+func Example() {
+	endpoint := "http://seed5.bridgeprotocol.io:10332"
+	opts := client.Options{}
+
+	c, err := client.New(context.TODO(), endpoint, opts)
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+
+	if err := c.Ping(); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+
+	resp, err := c.GetAccountState("ATySFJAbLW7QHsZGHScLhxq6EyNBxx3eFP")
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+	fmt.Println(resp.ScriptHash)
+	fmt.Println(resp.Balances)
+}