Add translated _admonition/gpu.md (#172)

mix_model.md on main and several resync branches (e.g. ifp_egm) include
_admonition/gpu.md, which never existed in this repo. Translated from
the English source's lectures/_admonition/gpu.md.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: mmcky

lectures/_admonition/gpu.md

@@ -0,0 +1,11 @@
+```{admonition} GPU
+:class: warning
+
+本讲座是在配有GPU的机器上构建的——不过没有GPU也可以运行。
+
+[Google Colab](https://colab.research.google.com/) 提供带GPU的免费套餐，使用方法如下：
+
+1. 点击右上角的"播放"图标
+2. 选择 Colab
+3. 将运行时环境设置为包含GPU
+```