Add release process

.github/workflows/release.yml

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+name: Release
+
+on:
+  push:
+    tags:
+      - "v[0-9]+.[0-9]+.[0-9]+"
+
+jobs:
+  publish:
+    permissions:
+      id-token: write
+      contents: read
+    uses: fastly/devex-reusable-workflows/.github/workflows/publish-rust-crates-io-v1.yml@main
+    with:
+      crate_name: esi
+      expected_version: ${{ github.ref_name }}

RELEASING.md

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+# Releasing
+
+1. **Create a release branch**:
+
+   ```sh
+   git checkout main
+   git pull
+   git checkout -b release/vX.Y.Z
+   ```
+
+2. **Update the version** in [Cargo.toml](Cargo.toml) under `[workspace.package]`:
+
+   ```toml
+   [workspace.package]
+   version = "X.Y.Z"
+   ```
+
+3. **Regenerate the lockfile**:
+
+   ```sh
+   cargo generate-lockfile
+   ```
+
+4. **Commit and push the version bump**:
+
+   ```sh
+   git add Cargo.toml Cargo.lock
+   git commit -m "Release vX.Y.Z"
+   git push -u origin release/vX.Y.Z
+   ```
+
+5. **Open a pull request** into `main` and get it merged.
+
+6. **Tag the release from `main`**:
+
+   ```sh
+   git checkout main
+   git pull
+   git tag vX.Y.Z
+   git push origin vX.Y.Z
+   ```
+
+   The tag must match the pattern `vX.Y.Z` and the version in `Cargo.toml`.
+
+7. **Monitor the release**. The [Release workflow](.github/workflows/release.yml) will automatically verify the tag matches the crate version and publish to [crates.io](https://crates.io/crates/esi).
+
+   You can follow progress in the **Actions** tab of the repository.