In my experience, putting up a single canonical webpage with clear authoritative info on the topic is pretty helpful – starting with a short and very-easy-to-read intro paragraph, that’s followed by a detailed tutorial/guide and then an FAQ and an email address/contact link to get further advice.
Then you have to advertise the news and link to that page, else people won’t necessarily look for it and find it; this can take anywhere from 30 minutes to weeks, depending on how crucial it is to get the word out and how much time you’re willing to spend on marginal utility. Some of the people you’re trying to reach pay attention to email newsletters, some to podcasts, some to Discords and other fora. Think about whom you’re trying to reach and what other hobby or professional groups/interests they may share – maybe in this case, for example, many of the projects you particularly want to reach are doing scientific/numerical stuff, so a bunch of of them are part of NumFOCUS or the SciPy and PyData conferences/meetups, so you can ask someone who’s in that world to forward stuff there. Or maybe there’s a cluster you’d like to reach in fintech, so you look for pre-existing interest groups there to send your link to.
Some places to start:
@smm heads-up in case any of this is useful to you as you construct more systematic playbooks for communicating out to the users of Python package distribution tools!
@encukou Apologies in advance if any of this is redundant and you knew it already.