I don't see the upside to it. Jobs are not 1:1 with code repositories. Jobs also don't get created/deleted in conjunction with code changes. It doesn't make sense to me to put this information in a repository when we have things like job boards already.
Forking and typosquatting. If, for example, Google is famous for HIRING.md and someone squats The username Goog1e with their own nefarious HIRING.md, it seems like a great vector for phishing.<p>Hiring scams are increasingly common since the pandemic, as far as I can personally gather from linkedin.
Pitfalls, sure. But also many advantages! Teams looking for new ppl can include in the relevant repos, more likely to be noticed than some career page.