Document release process

* bump version (dropping SNAPSHOT)
* create a release & a tag in GH web UI
* wait for GH action to pass
* go to https://s01.oss.sonatype.org/#stagingRepositories
* "close" the repository
* wait for the sonatype build to pass
* "release" the repository
* wait for maven central to update (https://central.sonatype.com/artifact/dev.zarr/jzarr/0.3.7/versions)
* profit