Ensure lib.rs code example in uefi crate is tested

[nicholasbishop]

We tried to use #![doc = include_str!("../../template/src/main.rs")], but that is causing the release job to fail: #1330 (comment)

As a quick workaround we will inline the example code, but that means it won't be tested and could break easily. Filing this issue to track fixing it.

[nicholasbishop]

Fixed in #1353