readme: add examples of usage SQL in connector

Added examples of using SQL queries in connector with
different types of arguments in README.md.

Follows up #62

Author: vr009

README.md

@@ -184,9 +184,6 @@ import (
 )
 
 func main() {
-	spaceNo := uint32(512)
-	indexNo := uint32(0)
-
 	server := "127.0.0.1:3013"
 	opts := tarantool.Opts{
 		Timeout:       500 * time.Millisecond,
@@ -285,6 +282,112 @@ func main() {
 }
 ```
 
+To use SQL to query a tarantool instance, call `Execute`. 
+
+Pay attention that with different types of queries (DDL, DQL, DML etc.) 
+some fields of the response structure (`MetaData` and `InfoAutoincrementIds` in `SQLInfo`) may be nil.
+
+See the [protocol](https://www.tarantool.io/en/doc/latest/dev_guide/internals/box_protocol/#responses-for-sql) explanation for details.
+
+```go
+package main
+
+import (
+	"github.com/tarantool/go-tarantool"
+	"log"
+	"time"
+)
+
+func main() {
+  server := "127.0.0.1:3013"
+  opts := tarantool.Opts{
+    Timeout:       500 * time.Millisecond,
+    Reconnect:     1 * time.Second,
+    MaxReconnects: 3,
+    User:          "test",
+    Pass:          "test",
+  }
+  client, err := tarantool.Connect(server, opts)
+  if err != nil {
+    log.Fatalf("Failed to connect: %s", err.Error())
+  }
+  
+  resp, err := client.Execute("CREATE TABLE SQL_TEST (id INTEGER PRIMARY KEY, name STRING)")
+  log.Println("Execute")
+  log.Println("Error", err)
+  log.Println("Code", resp.Code)
+  log.Println("Data", resp.Data)
+  log.Println("MetaData", resp.MetaData)
+  log.Println("SQL Info", resp.SQLInfo)
+
+  // there are 3 options to pass named parameters to an SQL query
+  sqlBind1 := map[string]interface{} {
+    "id":   1,
+    "name": "test",
+  }
+
+  sqlBind2 := struct {
+    Id   int
+    Name string
+  } {1, "test"}
+
+  type kv struct {
+    Key   string
+    Value interface{}
+  }
+
+  sqlBind3 := []kv {
+    kv{"id", 1},
+    kv{"name", "test"},
+  }
+
+  // the next usage
+  resp, err = client.Execute("SELECT id FROM SQL_TEST WHERE id=:id AND name=:name", sqlBind1)
+  log.Println("Execute")
+  log.Println("Error", err)
+  log.Println("Code", resp.Code)
+  log.Println("Data", resp.Data)
+  log.Println("MetaData", resp.MetaData)
+  log.Println("SQL Info", resp.SQLInfo)
+
+  // the same as
+  resp, err = client.Execute("SELECT id FROM SQL_TEST WHERE id=:id AND name=:name", sqlBind2)
+  log.Println("Execute")
+  log.Println("Error", err)
+  log.Println("Code", resp.Code)
+  log.Println("Data", resp.Data)
+  log.Println("MetaData", resp.MetaData)
+  log.Println("SQL Info", resp.SQLInfo)
+
+  // the same as
+  resp, err = client.Execute("SELECT id FROM SQL_TEST WHERE id=:id AND name=:name", sqlBind3)
+  log.Println("Execute")
+  log.Println("Error", err)
+  log.Println("Code", resp.Code)
+  log.Println("Data", resp.Data)
+  log.Println("MetaData", resp.MetaData)
+  log.Println("SQL Info", resp.SQLInfo)
+
+  // there are 2 options to pass positional arguments to an SQL query
+  resp, err = client.Execute("SELECT id FROM SQL_TEST WHERE id=? AND name=?", 1, "test")
+  log.Println("Execute")
+  log.Println("Error", err)
+  log.Println("Code", resp.Code)
+  log.Println("Data", resp.Data)
+  log.Println("MetaData", resp.MetaData)
+  log.Println("SQL Info", resp.SQLInfo)
+
+  // the same as
+  resp, err = client.Execute("SELECT id FROM SQL_TEST WHERE id=? AND name=?", []interface{}{2, "test"})
+  log.Println("Execute")
+  log.Println("Error", err)
+  log.Println("Code", resp.Code)
+  log.Println("Data", resp.Data)
+  log.Println("MetaData", resp.MetaData)
+  log.Println("SQL Info", resp.SQLInfo)
+}
+```
+
 To enable support of UUID in msgpack with [google/uuid](https://github.com/google/uuid),
 import tarantool/uuid submodule.
 ```go