doc: Initial add releases.md

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

README.md

@@ -291,6 +291,8 @@ As of 2022-04-05, the following cloud images are supported:
 Direct kernel boot to userspace should work with a rootfs from most
 distributions.
 
+Further details can be found in the [release documentation](docs/releases.md).
+
 ## Hot Plug
 
 Cloud Hypervisor supports hotplug of CPUs, passthrough devices (VFIO),

docs/releases.md

@@ -0,0 +1,103 @@
+# Release Documentation
+
+## Abstract
+
+This document provides guidance to users, downstream maintainers and
+any other consumers of the Cloud Hypervisor project, this document
+describes the release process, release cadence, stability expectations and
+related topics.
+
+## Basic Terms
+
+### Stability
+
+For Cloud Hypervisor the following areas are subject to stability guarantees:
+
+- [REST API](api.md#rest-api)
+- [Command line options](api.md#command-line-interface)
+- [Device Model](device_model.md)
+- Device tree, device list, ACPI, Hyper-V enlightenments and any other
+  features exposed to guest
+- KVM compatibility
+- Rust edition compatibility
+
+This list is incomplete but this document serves as a best effort guide to stability
+across releases.
+
+### Experimental features
+
+Experimental features are under active development and no guarantees are made about their stability.
+
+List of experimental features:
+
+- TDX
+- vfio-user
+- vDPA
+
+### Security
+
+Security fixes should be included in a new point release.
+
+For security issues an advisory will be published via the GitHub security advisory process along with the release. Watching the project on GitHub will notify you of those issues.
+
+## Releases
+
+### Versioning
+
+The versioning scheme uses `MAJOR.POINT` pattern:
+
+- `MAJOR` can introduce incompatible changes along with support for new features. Changes to the [API](api.md#rest-api),
+  [CLI options](api.md#command-line-interface) and [device model](device_model.md)
+  require a notice at least 2 releases in advance for the actual change to take
+  place.
+- `POINT` contains bug fixes and/or security fixes.
+
+### Major Release Cadence
+
+Cloud Hypervisor is under active development. A new major release is issued approximately
+every 6 weeks. Point releases are issued on demand, when important bug fixes are in
+the queue. A major release would receive bug fixes for the next two cycles (~12 weeks)
+and then be considered EOL.
+
+```
++ - Active release support
+E - EOL
+
+        2021                2022                2023 
+         |    |    |    |    |    |    |    |    | 
+18.0     |    |    |  ++++++++E
+19.0     |    |    |    |++++++++E
+20.0     |    |    |    |   ++++++++E
+21.0     |    |    |    |    | ++++++++E
+22.0     |    |    |    |    |    +++++++++E
+23.0     |    |    |    |    |    |  +++++++++E
+
+```
+
+### Major Release Stability Considerations
+
+Snapshot/restore support is not compatible across `MAJOR` versions.
+Live migration support is not compatible across `MAJOR` versions.
+
+### LTS Release Cadence
+
+A regular release is promoted to LTS every 12 months. An LTS release is supported for 18 months. This gives a 6 months window for users to move to the new LTS.
+
+```
++ - Active release support
+E - EOL
+
+        2022                2023               2024                 2025                2026
+         |    |    |    |    |    |    |    |    |    |    |    |    |    |    |    |    |
+23.0     |    |+++++++++++++++++++++++++++++E
+43.0     |    |    |    |    |    |+++++++++++++++++++++++++++++E
+63.0     |    |    |    |    |    |    |    |    |    |+++++++++++++++++++++++++++++E
+
+```
+
+### LTS Stablity Considerations
+
+An LTS release is just a `MAJOR` release for which point releases are made for
+longer following the same rules for what can be backported to a `POINT` release.
+The focus lays on critical and security bug fixes which are pulled at the
+maintainer's discretion.