docs: add RELEASING.md (#29)

* docs: add RELEASING.md

Document the manual release process so any maintainer can cut a
release without needing to ask. Linked from the README.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Apply suggestion from @bm1549

* chore: add markdown files to .npmignore

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Apply suggestion from @bm1549

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: bm1549

.npmignore

@@ -4,3 +4,4 @@ test.sh
 limitation.js
 eslint*
 *.sw?
+*.md

README.md

@@ -40,6 +40,11 @@ const diagnostics_channel = require('dc-polyfill');
 When a Pull Request is created the test suite runs against dozens of versions of Node.js. Notably, versions right before a change and versions right after a change, the first version of a release line, and the last version of a release line. To test locally it's recommended to use a node version management tool, such as `nvm`, to test changes with.
 
 
+## Releasing
+
+See [RELEASING.md](RELEASING.md) for the steps to publish a new version of `dc-polyfill` to npm.
+
+
 ## License / Copyright
 
 See [LICENSE.txt](LICENSE.txt) for full details.

RELEASING.md

@@ -0,0 +1,45 @@
+# Releasing
+
+`dc-polyfill` is published to npm as [`dc-polyfill`](https://www.npmjs.com/package/dc-polyfill). Releases are currently cut manually by a maintainer with publish access to the package on npm.
+
+## Prerequisites
+
+- Push access to `main` on this repository.
+- The [`gh`](https://cli.github.com/) CLI, authenticated against `DataDog/dc-polyfill`.
+- Log in to the npm account with publish access to `dc-polyfill`. Check with `npm whoami`; run `npm login` if needed. If you don't have publish access, ask an existing maintainer.
+
+## Cutting a release
+
+```sh
+# Make sure main is green and up to date.
+git checkout main
+git pull origin main
+
+# Bump the version. Pick patch, minor, or major per semver.
+# This updates package.json, creates a commit (e.g. "0.1.11"),
+# and creates a matching v0.1.11 tag locally.
+npm version patch
+
+# Sanity-check what will be packed before publishing anything public.
+npm publish --dry-run
+
+# Publish to npm. Do this before pushing the tag so a failed publish
+# doesn't leave a release tag in the repo that points at no npm version.
+npm publish
+
+# Push the version-bump commit and the tag.
+git push origin main --follow-tags
+
+# Create the GitHub release with autogenerated notes.
+gh release create "v$(node -p "require('./package.json').version")" --generate-notes
+```
+
+## Verifying the release
+
+```sh
+# Confirm the new version is live on npm.
+npm view dc-polyfill version
+
+# Confirm the GitHub release exists.
+gh release view "v$(node -p "require('./package.json').version")"
+```