Update README.md

Update README.md

Create TerrainRenderer.swift

Create ContentView.swift

Create TerrainExplorerApp.swift

Create ModelLoader.swift

Create MeshResource.swift

Create HeightfieldTerrain.swift

Create OrbitCameraController.swift

Create Camera.swift

Create SceneNode.swift

Create Scene.swift

Create MatrixExtensions.swift

Create ShaderTypes.swift

Create MetalView.swift