add documentation for releasing new rust core

[ctb]

what I did for r0.12.1, based on r0.12.0

# generate log of PRs
git log --oneline r0.12.0..latest src/core | cut -d\  -f2- > /tmp/out.txt

#edited src/core/CHANGELOG.md appropriately

# tagged, added commit messages
git tag -a r0.12.1

# pushed
git push origin r0.12.1

[ctb]

🤦 also probably want to bump version in src/core/Cargo.toml first.

[ctb]

viz

• MRG: bump rust core version to r0.12.1 #2988

[ctb]

🎉 https://crates.io/crates/sourmash

[luizirber]

There is also a changelog for the Rust crate in https://github.com/sourmash-bio/sourmash/blob/latest/src/core/CHANGELOG.md

[ctb]

checklist:

• verify minimum supported rust version (MSRV) for writing release notes (see MRG: bump rust core version to r0.12.1 #2988 for an example); MSRV is checked by CI in .github/workflows/rust.yml, minimum_rust_version
• write release notes using git log --oneline r0.12.0..latest src/core | cut -d\ -f2- > /tmp/out.txt
• verify that the ChangeLog is up to date: https://github.com/sourmash-bio/sourmash/blob/latest/src/core/CHANGELOG.md
• bump version in src/core/Cargo.toml
• run cargo build to update src/core/Cargo.lock

[ctb]

so as you can see from the above and from #3033 my process is:

• verify that all the items on the checklist are good to go
• update the things that need to be updated in a PR
• after the PR is merged, I will run the tagging that triggers github actions:

# tagged, added commit messages
git tag -a r0.13.0

# pushed
git push origin r0.13.0

[ctb]

example! #3199