[Suggestion] Add a warning when enabling profile-sync-daemon on systems with ≤8 GB RAM

One user on the Discord had problems starting apps due to `/run` being full.

This is because `logind` limits `/run` to 10% of total RAM by default. profile-sync-daemon puts the firefox profile in /run, which will only get bigger and bigger until it fully exhausts `/run` and anything else that needs to use it will fail to do so.

Although increasing the maximum `tmpfs` size is one option, adding a warning makes sense since low RAM systems already have limited headroom and enabling psd can further exhaust available RAM.