SendCutSend instructions for getting metal mount created

Since I've never used SendCutSend before, it'd be nice to have a step-by-step set of instructions for ordering the 2U faceplate in metal from them (mostly what options to choose), and notes about potential costs and shipping times.

(There is no rush to do this of course!)

Separately, maybe someone in the community would like to organize a group buy? Logistics mostly kill that sort of thing, but if multiple people in one small region might want metal parts, it would save money to have one person order multiples, then distribute them locally.

And with flat 10" parts, shipping costs aren't that bad.

首先检查 repository 中现有的 2U 面板文档以及当前关于 SendCutSend 的任何指南。记录订购选项、可能的费用、运输时间，以及任何有明确支持依据的团购说明；当读者能够按照步骤订购金属部件时，这项工作就完成了。

由索引模型根据 Issue 内容生成。