Fix wording

[godunko]

PR creation checklist

• A test is included, if required by the changes.
• doc/user-changes.md has been updated, if there are user-visible changes.
• doc/catalog-format-spec.md has been updated, if applicable.
• BREAKING.md has been updated for major changes in alr, minor/major in catalog format.

[mosteo]

This is kind of fuzzy. A crate is only the name (mycrate) whereas a release includes a version. On disk, you always have a particular version, so even if its a temporary one, its closer to a release than simply a crate. It's true that people use them interchangeably, or default to crate even when talking about releases...