Auto merge of #9224 - ehuss:split-debuginfo-docs, r=Eh2406
Auto merge of #9224 - ehuss:split-debuginfo-docs, r=Eh2406

Update split-debuginfo docs around the default.

The default behavior was changed during the course PR #9112, but the docs weren't updated.

Closes #9218

nipunn1313/cargo,rust-lang/cargo,eminence/cargo,rustyhorde/cargo,rust-lang/cargo,rust-lang/cargo,eminence/cargo,eminence/cargo,nipunn1313/cargo,eminence/cargo,rustyhorde/cargo,rust-lang/cargo,rustyhorde/cargo,nipunn1313/cargo,rustyhorde/cargo,nipunn1313/cargo