docs: add RELEASING.md release guide

README.md

@@ -6,4 +6,6 @@ Please see the [README](rodbus/README.md) for information on the core Rust libra
 
 A user guide and documentation may be found [here](https://stepfunc.io/products/libraries/modbus/). 
 
-Refer to the [CHANGELOG](CHANGELOG.md) for a release history.
+Refer to the [CHANGELOG](CHANGELOG.md) for a release history.
+
+Maintainers: see [RELEASING.md](RELEASING.md) for how to cut a release.

RELEASING.md

@@ -0,0 +1,62 @@
+# Releasing
+
+How to cut a release of Rodbus. Same steps for release candidates (`1.5.0-RC1`)
+and final releases (`1.5.0`).
+
+A release is driven by **pushing a git tag**. CI does the publishing (crates.io,
+Maven Central, NuGet, docs, and a draft GitHub release). Your job is to land a
+"Release X.Y.Z" commit on `main`, then tag it.
+
+## 1. Prepare the release commit (on a branch)
+
+```bash
+OLD=1.5.0-RC2
+NEW=1.5.0
+
+# Bump the version in every crate, FFI binding build file, and the guide.
+grep -rln "$OLD" --include="*.toml" --include="*.txt" --include="*.json" \
+  --include="*.csproj" --include="*.xml" . | grep -v Cargo.lock | \
+  while read f; do sed -i "s/${OLD//./\\.}/$NEW/g" "$f"; done
+
+# Pull in the latest semver-compatible dependency versions. The FFI binaries
+# ship compiled against whatever is in Cargo.lock, so bake in the latest patches
+# (and keep `cargo audit` meaningful). Review the diff before committing.
+cargo update
+```
+
+- Update the top `CHANGELOG.md` header to `### X.Y.Z ###` and add entries for
+  user-facing changes since the last release (skip CI-only changes).
+- Don't forget `guide/sitedata.json` — it holds the version the published guide
+  renders. (The grep above catches it; just verify.)
+- Confirm nothing is left behind: `grep -rn "$OLD" . | grep -vE "/target/|\.git/"`
+  should print nothing.
+
+## 2. Verify, then merge
+
+```bash
+cargo check --workspace
+cargo audit          # must pass; resolve any advisories before releasing
+```
+
+Open a PR titled `Release X.Y.Z` against `main`, get CI green, and merge.
+
+## 3. Tag the release
+
+The tag name **must exactly match** the version in `Cargo.toml` — CI derives the
+published version from it. Bare semver, no `v` prefix; RCs as `X.Y.Z-RCn`.
+
+```bash
+git checkout main && git pull
+git tag -a 1.5.0 -m "Release 1.5.0"
+git push origin 1.5.0
+```
+
+## 4. Finish up
+
+- Watch the tagged CI run. The publish jobs are idempotent, so a re-push of the
+  same tag safely retries after a transient failure.
+- CI opens the GitHub release as a **draft** — review the artifacts, paste in the
+  changelog section, and publish it.
+
+> This pipeline mirrors `stepfunc/dnp3`; port release-process fixes between the
+> two repos.