Mark repo unmaintained or call for maintainers

[alextes]

I get it; you are busy!
When a repo gets to a point where the low-review-effort PRs go stale it might be a good idea to be explicit about the repo being unmaintained or asking if people are willing to help out.

There is an issue that warns about a - now fixed - vulnerability, bad docs, and a deprecated dependency. This package is still downloaded 150K times a month. Let's maintain it or clearly state it isn't 😄. Both could help this repo back to life making a significant positive change for the ecosystem.

/cc @indexzero

[mostlyjason]

Loggly does not maintain this repo, but it does maintain it's official fork https://github.com/loggly/node-loggly-bulk