Find out a way to upload arbitrary hotfixes to the user guide

[rami3l]

Problem you are trying to solve

As discussed in https://rust-lang.zulipchat.com/#narrow/channel/490103-t-rustup/topic/stable.20docs/near/558754674, there are times when we want to update the stable user guide without doing the full release.

Currently this is not trivially feasible, e.g. #4613 has failed due to rust-lang/rust's CI structure changes accumulated over time.

Solution you'd like

one hack that I can think about is to use a very specific format for book hotfixes for the pipeline to detect, so that such commits will not trigger the actual build of the binaries[...]

Notes

No response