Improve docs for embed-bitcode and linker-plugin-lto
Improve docs for embed-bitcode and linker-plugin-lto

Follow-up from #71716 I wasn't able to add in time.

graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust