This branch updates CONTRIBUTING.md to document how to release
a new version of a Tracing crate, and adds the `publish` shell script
from the `tokio-rs/tokio` repo to aid in the release process.
I've also updated references in CONTRIBUTING.md to refer to Tracing
rather than Tokio Trace.
* docs: add release section to CONTRIBUTING.md
* add publish script
* docs: remove references to tokio-trace/nursery
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
