New review comment by Minoru on void-packages repository

https://github.com/void-linux/void-packages/pull/28801#discussion_r577898470

Comment:
JFYI: I recommend `/dev/shm` in the README because tests create a lot of temporary files, and putting them onto a tmpfs (of which `/dev/shm` is a common instance) greatly speeds things up. If you're tight on RAM or don't need the extra speed, or if `/tmp` is already a tmpfs, using `/tmp` is fine.