Update build instructions for all platforms

Added separate build instructions for Linux/macOS and Windows to the README for improved clarity and guidance.

Author: lijy91

README.md

@@ -45,6 +45,9 @@ sudo dnf install gtk3-devel
 git clone https://github.com/libnativeapi/nativeapi.git
 cd nativeapi
 ```
+
+#### Linux/macOS
+
 ```bash
 # Create build directory
 mkdir build
@@ -55,6 +58,18 @@ cmake ..
 cmake --build . --config Release
 ```
 
+#### Windows
+
+```powershell
+# Create build directory
+mkdir build
+cd build
+
+# Configure and build
+cmake ..
+cmake --build . --config Release
+```
+
 ## Development
 
 ### Code Formatting