Include safety comments on unsafe blocks in chapter 3?

[helixbass]

Type of error

Minor technical mistake

Location of the error

https://marabos.nl/atomics/memory-ordering.html#fences

Description of the error

In the "Let’s take a look at a more complicated use case of release and acquire fences" example, there are no // safety: ... comments on the unsafe blocks

I was finding the safety comments on other unsafe blocks to be helpful and I know this is considered a best practice so seems worth pointing out their absence here