Link published simulation code and tested checkout revision

USAGE.md

@@ -2,16 +2,24 @@
 
 Models: https://huggingface.co/Berkeley-ICON-Lab/ALTER-models
 Data and provenance: https://huggingface.co/datasets/Berkeley-ICON-Lab/ALTER-data
-Code project: https://github.com/labicon/ALTER
+Code: https://github.com/labicon/ALTER/tree/e180a013e30d7b7c5478e029229ff9cd3154028e
 
-The artifact upload precedes publication of the prepared code branch. At this
-stage the GitHub default branch may still contain only the project website.
+The simulation code is public on `release/alter-port-20260929`. The default
+branch may still contain only the website while the code awaits merge.
 Both artifact uploads are complete. release-manifest.json records immutable
 artifact revisions and checksums. bundle-index.json and SHA256SUMS list this
 repository’s artifact contents. The manifest pins the commits containing the
 artifacts, which precede this documentation commit.
 
-Once the code release is available, from its repository root run:
+Check out the tested code revision and follow its [installation guide](https://github.com/labicon/ALTER/blob/e180a013e30d7b7c5478e029229ff9cd3154028e/documentation/release/installation.md):
+
+```bash
+git clone https://github.com/labicon/ALTER.git
+cd ALTER
+git checkout e180a013e30d7b7c5478e029229ff9cd3154028e
+```
+
+Then, from the repository root run:
 
 ```bash
 python scripts/download_release.py --manifest release/manifest.json \