docs: Document the current release process (#2745)

docs/release_process.md

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+---
+myst:
+  heading_anchors: 4
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+
 # Release Process
 
+The Singer SDK currently follows roughly a [ZeroVer versioning scheme](https://0ver.org/). Starting with the Singer SDK 1.0, version numbers will use [semantic versioning](https://semver.org/).
+
 ## PyPI releases
 
-Releases are published to PyPI by a GitHub Actions workflow, triggered when a GitHub [Release](https://github.com/meltano/sdk/releases) is published.
+### Stable releases
+
+The following steps are required to create a stable release:
+
+1. Trigger the `.github/workflows/version_bump.yml` workflow from the GitHub Actions tab, or from the CLI with `gh workflow run version_bump.yml`.
+2. Wait for the workflow to complete. It will create a new PR with the version bump, and also a draft release.
+3. Review the PR for any errors in the changelog and version bumps, then merge it.
+4. Publish the draft release from the GitHub Releases tab.
 
-### Feature releases
+#### Feature releases
 
 Feature releases are the primary way that new features are added to the Singer SDK. They are released on a roughly monthly cadence.
 
-### Patch releases
+#### Patch releases
 
 Patch releases are released as needed to fix bugs or security issues. They are released on an as-needed basis.
 
-## Release cadence
+#### Release Highlights
+
+Once the release is published, we manually add a section to the changelog with the release highlights. This section should include a brief description of the most important changes in the release. For example:
+
+```markdown
+## v0.41.0 (2024-10-02)
+
+### Highlights
 
-Starting with the Singer SDK 1.0, version numbers will use a loose form of [semantic versioning](https://semver.org/).
+- It's easier now for SQL tap developers to customize the mapping from SQL column types to JSON schema. See [the guide](https://sdk.meltano.com/en/v0.41.0/guides/sql-tap.html#custom-type-mapping) for details.
+```
+
+### Pre-releases
+
+```bash
+git tag v0.42.0a3
+git push origin v0.42.0a3
+```
+
+Pre-releases are normal tags with pre-release identifiers. They are used to test new features before a stable release. Pre-releases are triggered by pushing a tag with a pre-release identifier, e.g. `v0.42.0a3`.
+
+We don't generate release notes for pre-releases, nor do we update the changelog so creating a pre-release is as simple as pushing a tag:
+
+## Release cadence
 
-SemVer makes it easier to see at a glance how compatible releases are with each other. It also helps to anticipate when compatibility shims will be removed.
+The Singer SDK follows a roughly monthly release cadence. [Milestones](https://github.com/meltano/sdk/milestones) are used to track the progress of each release. The milestones are named after the release version, e.g. `v0.42.0`.
 
 ## Deprecation policy
 
 A [feature release](#feature-releases) may deprecate a feature, but it will not remove it until the next major release. A deprecation will be clearly documented in the changelog and in the code.
 
-All deprecated features will emit a `SingerDeprecationWarning` when used, so users can raise them as exceptions when running their tests to ensure that they are not using any deprecated features:
+All deprecated features will emit a `SingerSDKDeprecationWarning` when used, so users can raise them as exceptions when running their tests to ensure that they are not using any deprecated features:
 
 ```console
-$ pytest -W error::singer_sdk.utils.deprecation.SingerSDKDeprecationWarning
+$ pytest -W error::singer_sdk.helpers._compat.SingerSDKDeprecationWarning
 ```