docs: update README

Closes #TNTP-3736

Author: patapenka-alexey

README.md

@@ -22,8 +22,16 @@ high performance due to:
 * [Installation](#installation)
 * [Documentation](#documentation)
 * [Quick start](#quick-start)
+  * [Using pre-generated optional types](#using-pre-generated-optional-types)
+  * [Usage with go-tarantool](#usage-with-go-tarantool)
 * [Gentype Utility](#gentype-utility)
+  * [Overview](#overview)
+  * [Features](#features)
+  * [Gentype installation](#gentype-installation)
+  * [Generating Optional Types](#generating-optional-types)
+  * [Using Generated Types](#using-generated-types)
 * [Development](#development)
+  * [Run tests](#run-tests)
 * [License](#license)
 
 ## Installation
@@ -32,48 +40,46 @@ high performance due to:
 go install github.com/tarantool/go-option@latest
 ```
 
+## Documentation
+
+You could run the `godoc` server on `localhost:6060` with the command:
+
+```shell
+make godoc_run
+```
+
+And open the generated documentation in another terminal or use the
+[link][godoc-url]:
+
+```shell
+make godoc_open
+```
+
 ## Quick start
 
-```Go
-package main
+### Using pre-generated optional types
 
-import (
-	"bytes"
-	"fmt"
+Generated types follow the pattern Optional<TypeName> and provide methods for working
+with optional values:
 
-	"github.com/tarantool/go-option"
-	msgpack "github.com/vmihailenco/msgpack/v5"
-)
+```go
+// Create an optional with a value.
+opt := SomeOptionalString("hello")
 
-func main() {
-	var buf bytes.Buffer
-
-	enc := msgpack.NewEncoder(&buf)
-	dec := msgpack.NewDecoder(&buf)
-
-	someUint := option.SomeUint(12)
-	err := someUint.EncodeMsgpack(enc)
-	if err != nil {
-		panic("encode fail")
-	}
-
-	var unmarshaled option.Uint
-	err = unmarshaled.DecodeMsgpack(dec)
-	if err != nil {
-		panic(fmt.Errorf("decode fail: %s", err))
-	}
-
-	if !unmarshaled.IsSome() {
-		panic("IsSome error")
-	}
-
-	if unmarshaled.Unwrap() != 12 {
-		panic("Unwrap error")
-	}
+// Check if a value is present.
+if opt.IsSome() {
+    value := opt.Unwrap()
+    fmt.Println(value)
 }
+
+// Use a default value if none.
+value := opt.UnwrapOr("default")
+
+// Encode to MessagePack.
+err := opt.EncodeMsgpack(encoder)
 ```
 
-## Usage with go-tarantool
+### Usage with go-tarantool
 
 It may be necessary to use an optional type in a structure. For example,
 to distinguish between a nil value and a missing one.
@@ -145,17 +151,15 @@ while ensuring proper encoding and decoding when using MessagePack.
 - Full MessagePack `CustomEncoder` and `CustomDecoder` implementation
 - Type-safe operations
 
-### Installation
+### Gentype installation
 
 ```bash
 go install github.com/tarantool/go-option/cmd/gentypes@latest
 # OR (for go version 1.24+)
 go get -tool github.com/tarantool/go-option/cmd/gentypes@latest
 ```
 
-### Usage
-
-#### Generating Optional Types
+### Generating Optional Types
 
 To generate optional types for existing types in a package:
 
@@ -179,7 +183,7 @@ Flags:
 -128 and 127, no default value)
 • `-verbose`: Enable verbose output (default: `false`)
 
-#### Using Generated Types
+### Using Generated Types
 
 Generated types follow the pattern Optional<TypeName> and provide methods for working
 with optional values:
@@ -199,7 +203,6 @@ value := opt.UnwrapOr("default")
 
 // Encode to MessagePack.
 err := opt.EncodeMsgpack(encoder)
-```
 
 ## Development
 
@@ -216,27 +219,12 @@ make coverage
 
 ### Run tests
 
-To run default set of tests:
+To run default set of tests directly:
 
 ```shell
 go test ./... -count=1
 ```
 
-### Documentation
-
-You could run the `godoc` server on `localhost:6060` with the command:
-
-```shell
-make godoc_run
-```
-
-And open the generated documentation in another terminal or use the
-[link][godoc-url]:
-
-```shell
-make godoc_open
-```
-
 ## License
 
 BSD 2-Clause License