This simplifies the PR template, which is a bit cumbersome, and instead
replaces it with a simpler notice that includes a template sign-off and
a new `CONTRIBUTING.md` document.
Signed-off-by: Neil Twigg <neil@nats.io>
Co-authored-by: Byron Ruth <byron@nats.io>
* We've renamed our default branch from 'master' to 'main'
* We switched some time ago from 'gnatsd' to 'nats-server' and some temporary
redirects no longer work, so fix those too