Add notes on getting the HDC of a window on Win32

Related to #1913.

include/GLFW/glfw3native.h

@@ -161,6 +161,14 @@ GLFWAPI const char* glfwGetWin32Monitor(GLFWmonitor* monitor);
  *  @return The `HWND` of the specified window, or `NULL` if an
  *  [error](@ref error_handling) occurred.
  *
+ *  @remark The `HDC` associated with the window can be queried with the
+ *  [GetDC](https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getdc)
+ *  function.
+ *  @code
+ *  HDC dc = GetDC(glfwGetWin32Window(window));
+ *  @endcode
+ *  This DC is private and does not need to be released.
+ *
  *  @thread_safety This function may be called from any thread.  Access is not
  *  synchronized.
  *
@@ -177,6 +185,14 @@ GLFWAPI HWND glfwGetWin32Window(GLFWwindow* window);
  *  @return The `HGLRC` of the specified window, or `NULL` if an
  *  [error](@ref error_handling) occurred.
  *
+ *  @remark The `HDC` associated with the window can be queried with the
+ *  [GetDC](https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getdc)
+ *  function.
+ *  @code
+ *  HDC dc = GetDC(glfwGetWin32Window(window));
+ *  @endcode
+ *  This DC is private and does not need to be released.
+ *
  *  @thread_safety This function may be called from any thread.  Access is not
  *  synchronized.
  *