docs(README): add backport link

Author: ErichDonGubler

CHANGELOG.md

@@ -48,7 +48,7 @@ Bottom level categories:
 
 #### DX12
 
-- Align copies b/w textures and buffers via a single intermediate buffer per copy when `D3D12_FEATURE_DATA_D3D12_OPTIONS13.UnrestrictedBufferTextureCopyPitchSupported` is `false`. By @ErichDonGubler in [#7721](https://github.com/gfx-rs/wgpu/pull/7721).
+- Align copies b/w textures and buffers via a single intermediate buffer per copy when `D3D12_FEATURE_DATA_D3D12_OPTIONS13.UnrestrictedBufferTextureCopyPitchSupported` is `false`. By @ErichDonGubler in [#7721](https://github.com/gfx-rs/wgpu/pull/7721), backported in [#8374](https://github.com/gfx-rs/wgpu/pull/8374).
 
 #### Naga