Add notes for bumping version as part of a release (#27080)

### Description
<!-- Describe your changes. -->
When creating a release branch for a new ORT release, there are some
steps required to comprehensively update the version number across the
codebase. This change adds the steps for that for anyone driving a
release.


### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
This will help with the release process and ensure that any bits
produced from release branches carry the right version information.

---------

Co-authored-by: Aditya Rastogi <adityar@ntdev.microsoft.com>

Author: adrastogi

docs/Versioning.md

@@ -11,6 +11,67 @@ The version number of the current stable release can be found
 ## Release cadence
 See [Release Management](ReleaseManagement.md)
 
+## Updating the Version for a Release
+
+When preparing a release, follow these steps to update the version number across the codebase. This applies both when creating an initial release branch (updating `main`) and when preparing patch releases on release branches:
+
+### Prerequisites
+- Node.js (check [js/.nvmrc](../js/.nvmrc) for the required version)
+- npm (comes with Node.js)
+- Python 3
+
+Verify your setup:
+```bash
+node --version   # Should match the version in js/.nvmrc
+npm --version    # Should be v8.0 or newer
+```
+
+### Steps
+
+1. **Update the VERSION_NUMBER file**
+
+   Edit [VERSION_NUMBER](../VERSION_NUMBER) in the repository root to reflect the new version (e.g., `1.23.3`).
+
+2. **Run the version update script**
+
+   From the repository root, run:
+   ```bash
+   python tools/python/update_version.py
+   ```
+
+   This script automatically updates version numbers in:
+   - `docs/Versioning.md` - Adds a new row to the version table
+   - `docs/python/README.rst` - Adds release notes entry
+   - `onnxruntime/__init__.py` - Python package version
+   - `js/` packages - All NPM package versions and lock files
+
+3. **Update the C API static_assert (Manual Step)**
+
+   The script does **not** update the version check in the C API. You must manually update the `static_assert` in [onnxruntime/core/session/onnxruntime_c_api.cc](../onnxruntime/core/session/onnxruntime_c_api.cc).
+
+   Search for `static_assert(std::string_view(ORT_VERSION)` and update the version string:
+   ```cpp
+   static_assert(std::string_view(ORT_VERSION) == "X.Y.Z",
+                 "ORT_Version change detected, please follow below steps to ensure OrtApi is updated properly");
+   ```
+
+   Replace `X.Y.Z` with your new version number. The comments following this assert explain additional steps if new APIs were added to this release.
+
+4. **Review all changes**
+
+   Review all modified files. Verify:
+   - Version numbers are correct in all updated files
+   - The release notes URL format is correct (e.g., `https://github.com/Microsoft/onnxruntime/releases/tag/vX.Y.Z`)
+
+5. **Commit and create PR**
+
+   Commit all changes and create a PR targeting `main` or a release branch as appropriate.
+
+### Notes
+
+- The version table in this file and the ONNX opset compatibility information on [onnxruntime.ai](https://onnxruntime.ai/docs/reference/compatibility.html#onnx-opset-support) are the canonical sources for version compatibility information.
+- For ONNX version/opset/IR reference numbers, see the [ONNX Versioning documentation](https://github.com/onnx/onnx/blob/main/docs/Versioning.md#released-versions).
+
 # Compatibility
 
 ## Backwards compatibility