docs: update RHI API docs

docs/api/rhi/d3d12/device/create-buffer.md

@@ -0,0 +1,32 @@
+# D3D12Device::CreateBuffer
+
+```cpp
+RHIBuffer* CreateBuffer(const BufferDesc& desc) override;
+```
+
+创建 D3D12 缓冲区资源。
+
+**参数：**
+- `desc` - 缓冲区描述符，包含大小、类型、标志等
+
+**返回：** 新创建的缓冲区指针，失败返回 `nullptr`
+
+**复杂度：** O(1)
+
+**示例：**
+
+```cpp
+BufferDesc bufferDesc;
+bufferDesc.size = sizeof(Vertex) * vertexCount;
+bufferDesc.stride = sizeof(Vertex);
+bufferDesc.bufferType = (uint32_t)BufferType::Vertex;
+bufferDesc.flags = 0;
+
+RHIBuffer* vertexBuffer = device->CreateBuffer(bufferDesc);
+```
+
+## 相关文档
+
+- [D3D12Device 总览](device.md) - 返回类总览
+- [RHIDevice::CreateBuffer](../../device/create-buffer.md) - 基类方法
+- [D3D12Buffer](../../buffer/buffer.md) - D3D12 缓冲区实现