add release action

docs/RELEASES.md

@@ -0,0 +1,60 @@
+# Release Builds
+
+The GitHub Actions workflow in `.github/workflows/release.yml` builds ready-to-use Linux x86_64 dynamic module packages.
+
+## Manual Release Only
+
+The workflow runs only through GitHub Actions `workflow_dispatch`. It does not run on pushes, pull requests, or tag pushes.
+
+Open the workflow in GitHub Actions and choose:
+
+- `nginx_versions`: space-separated versions, for example `1.24.0 1.26.3 1.28.0`
+- `version_bump`: `patch`, `minor`, or `major`
+- `push_image`: whether to push the Docker image to GHCR
+
+The workflow fetches existing `vMAJOR.MINOR.PATCH` tags, computes the next semantic version, creates an annotated tag, pushes it, and publishes the GitHub release.
+
+Examples:
+
+```text
+latest v1.2.3 + patch = v1.2.4
+latest v1.2.3 + minor = v1.3.0
+latest v1.2.3 + major = v2.0.0
+no existing tag + patch = v0.0.1
+```
+
+## Built Nginx Versions
+
+By default, the workflow builds packages for:
+
+- Nginx 1.24.0
+- Nginx 1.26.3
+- Nginx 1.28.0
+
+Each release asset is named like:
+
+```text
+ngx_http_monitoring_module-1.0.0-v1.0.0-nginx-1.28.0-linux-x86_64.tar.gz
+```
+
+Each package contains:
+
+- `modules/ngx_http_monitoring_module.so`
+- `INSTALL.md`
+- `METADATA.txt`
+- `SHA256SUMS`
+- example config
+- API/config/performance docs
+
+## Docker Image
+
+When `push_image` is true, the workflow also builds and pushes:
+
+```text
+ghcr.io/<owner>/<repo>:<tag>
+ghcr.io/<owner>/<repo>:latest
+```
+
+## Compatibility Warning
+
+Nginx dynamic modules are ABI-sensitive. The release packages are built with `--with-compat` on Ubuntu 22.04 against the Nginx version in the filename. Use the matching Nginx version and a compatible Linux/glibc runtime. Rebuild locally when using a vendor Nginx package with materially different module ABI or hardening options.