add release instructions

RELEASING.md

@@ -0,0 +1,32 @@
+# Releasing
+
+Releasing involves upgrading dependencies, bumping versions,
+tagging in git, and publishing to crates.io. 
+
+### Upgrading dependencies
+
+Using VS Code and [the crates extension](https://marketplace.visualstudio.com/items?itemName=serayuzgur.crates), upgrade any outdated dependencies.
+
+Commit this change to current release branch.
+
+### Release new version
+
+```
+cargo set-version --bump patch
+VERSION="$(tomlq -r .package.version Cargo.toml)"
+git add Cargo.toml Cargo.lock
+git commit -m "release $VERSION"
+git merge main
+git checkout main
+git merge dev
+git tag "$VERSION"
+git checkout dev
+cargo set-version --bump alpha
+NEW_VERSION="$(tomlq -r .package.version Cargo.toml)"
+git add Cargo.toml Cargo.lock
+git commit -m "a new version appears: $NEW_VERSION
+```
+
+### Publish to crates.io
+
+cargo publish