Add RELEASE-Github.md documentation

Author: ekaf

RELEASE-Github.md

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+# RELEASE-Github.md: Automated Release Workflow
+
+This document details the operation of the NLTK GitHub Actions release workflow, defined in `.github/workflows/release.yml`. This workflow automates the creation of GitHub releases and supports optional PyPI integration for official distribution.
+
+### Workflow Trigger
+
+The workflow is **event-driven**. It is automatically initiated upon pushing a git tag that follows the `v` prefix naming convention to the repository.
+
+* **Trigger Action:** `git push origin v3.10.x-rc`
+* **Requirement:** The workflow file must be present on the target branch. **Crucially, the release tag must point to a commit located within `origin/develop` to ensure the release is built from the authorized development head.**
+
+### Prerequisites & Permissions
+
+Successful execution of this workflow requires specific repository configurations:
+
+* **Write Permissions:** The workflow interacts with the GitHub API to draft releases and create tags; therefore, the triggering actor must have **write** access to the repository.
+* **Fork Execution:** If executing within a fork, ensure the repository settings under **Actions > General > Workflow permissions** are set to "Read and write permissions" to allow the workflow to create release objects.
+* **Secrets:** Ensure all necessary environment secrets (e.g., `PYPI_API_TOKEN` for package publishing) are correctly configured in the repository's secret store.
+
+### Release Strategy: GitHub vs. PyPI
+
+The workflow maintains a clear separation between testing and production release artifacts:
+
+| Stage | Platform | Purpose |
+| --- | --- | --- |
+| **Release Candidate** | GitHub Releases | Early community feedback and environment validation. |
+| **Official Release** | PyPI | Production distribution via `pip` and package repository indexing. |
+
+> **Integration:** While the workflow primarily stages artifacts on GitHub, it is capable of handling **PyPI integration**. If configured, the workflow will automatically publish the build artifacts to PyPI upon successful validation of the release tag.
+
+### Execution & Verification
+
+1. **Initiate Release:** Trigger the workflow by pushing the appropriate tag to the remote:
+```bash
+git tag v3.10.x-rc
+git push origin v3.10.x-rc
+
+2. **CI Validation:** As implemented in **[#3506](https://github.com/nltk/nltk/pull/3506)**, the workflow performs an automated check to verify that Continuous Integration (CI) has successfully passed on the specific commit to which the release tag points.
+3. **Monitor Logs:** Follow the execution progress in the repository’s **Actions** tab.
+4. **Audit:** If the workflow fails to push to PyPI or draft a release, inspect the logs for:
+   * **CI Failures:** Verify the commit status matches the requirements set forth in PR #3506.
+   * **Branch Validation:** Ensure the tagged commit is reachable via `origin/develop`.
+   * **Authentication errors:** Verify that the `PYPI_API_TOKEN` is active and has the correct scope.
+   * **Permission errors:** Confirm that the `GITHUB_TOKEN` has been granted the necessary write access.
+   * **Version conflicts:** Ensure the tag is not already associated with an existing release.