fixed README

README.md

@@ -7,17 +7,15 @@ vz provides the power of the Apple Virtualization.framework in Go. Put here is b
 
 > The Virtualization framework provides high-level APIs for creating and managing virtual machines (VM) on Apple silicon and Intel-based Mac computers. Use this framework to boot and run macOS or Linux-based operating systems in custom environments that you define. The framework supports the [Virtual I/O Device (VIRTIO)](https://docs.oasis-open.org/virtio/virtio/v1.1/csprd01/virtio-v1.1-csprd01.html) specification, which defines standard interfaces for many device types, including network, socket, serial port, storage, entropy, and memory-balloon devices.
 
-## USAGE
+## Usage
 
 Please see the [example](https://github.com/Code-Hex/vz/tree/main/example) directory.
 
-## REQUIREMENTS
+## Requirements
 
 - Higher or equal to macOS Big Sur (11.0.0).
 - Latest version of vz supports last two Go major [releases](https://go.dev/doc/devel/release) and might work with older versions.
 
-Deprecated older versions (v1, v2).
-
 ## Installation
 
 Initialize your project by creating a folder and then running `go mod init github.com/your/repo` ([learn more](https://go.dev/blog/using-go-modules)) inside the folder. Then install vz with the go get command:
@@ -26,6 +24,8 @@ Initialize your project by creating a folder and then running `go mod init githu
 $ go get github.com/Code-Hex/vz/v3
 ```
 
+Deprecated older versions (v1, v2).
+
 ## Feature Overview
 
 - ✅ Virtualize Linux on a Mac **(x86_64, arm64)**
@@ -40,7 +40,7 @@ $ go get github.com/Code-Hex/vz/v3
 - ✅ [Virtio Sockets](https://github.com/Code-Hex/vz/wiki/Sockets)
 - ✅ Less dependent (only under golang.org/x/*)
 
-## IMPORTANT
+## Important
 
 For binaries used in this package, you need to create an entitlements file like the one below and apply the following command.
 
@@ -90,6 +90,26 @@ You can check the version of the Xcode SDK available for each macOS on this site
 
 https://xcodereleases.com/
 
+## Version compatibility check
+
+The package provides a mechanism for checking the availability of the respective API through error handling:
+
+```go
+bootLoader, err := vz.NewEFIBootLoader()
+if errors.Is(err, vz.ErrUnsupportedOSVersion) || errors.Is(err, ErrBuildTargetOSVersion) {
+  return fallbackBootLoader()
+}
+if err != nil {
+  return nil, err
+}
+return bootLoader, nil
+```
+
+There are two items to check.
+
+1. API is compatible with the version of macOS
+2. The binary was built with the API enabled
+
 ## Knowledge for the Apple Virtualization.framework
 
 There is a lot of knowledge required to use this Apple Virtualization.framework, but the information is too scattered and very difficult to understand. In most cases, this can be found in [the official documentation](https://developer.apple.com/documentation/virtualization?language=objc). However, the Linux kernel knowledge required to use the feature provided by this framework is not documented. Therefore, I have compiled the knowledge I have gathered so far into this wiki.