Merge pull request #645 from jmtd/4846-ubi10-readme

[OPENJDK-4846] ubi10 readme

Author: jmtd

README.adoc

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+# Red Hat UBI OpenJDK container images
+
+These are the Red Hat Universal Base Image (UBI) OpenJDK container images,
+suitable for use with OpenShift Container Platform.
+
+→ [API Docs](https://rh-openjdk.github.io/redhat-openjdk-containers/)
+
+## Acquiring the Images
+
+### From [Red Hat Container Catalog](https://catalog.redhat.com/en):
+
+_Make sure you are viewing the most recent tag for each container_.
+
+* [ubi10/openjdk-25](https://catalog.redhat.com/software/containers/ubi10/openjdk-25/690ca440f43a9c6b120b2970?image=6a1789a7b0f39e62fd2fe614)
+* [ubi10/openjdk-21](https://catalog.redhat.com/software/containers/ubi10/openjdk-21/690ca3318f730aed0b1497fd?image=6a1789a84539c58e9ccddc58)
+* [ubi10/openjdk-25-runtime](https://catalog.redhat.com/software/containers/ubi10/openjdk-25-runtime/690ca3e4c827022925ed2db5?image=6a1789a2c84ec7f9491c341a)
+* [ubi10/openjdk-21-runtime](https://catalog.redhat.com/software/containers/ubi10/openjdk-21-runtime/690ca3b700d71ac7397b98c6?image=6a1789a4e30e09c84ec6c7e7)
+
+The UBI10-based OpenJDK images are available under the terms of the [UBI
+EULA](https://www.redhat.com/en/about/red-hat-end-user-license-agreements#UBI).
+
+[Red Hat provide Product documentation for
+customers](https://access.redhat.com/documentation/en-us/openjdk/25).
+Tables of environment variables used for image configuration are
+published to <https://rh-openjdk.github.io/redhat-openjdk-containers/>.
+These tables are automatically updated for every tagged release, and
+every commit to the development branches.
+
+Sources for older RHEL-based images are in the `ubi9`, `ubi8` and
+`rhel7`
+branches respectively.
+
+## How to build the images
+
+You need to [install
+Cekit](https://docs.cekit.io/en/latest/handbook/installation/index.html)
+to build these images.
+
+These sources are prepared and tested for CeKit 4.16.0.
+
+Example invocation to build `ubi10/openjdk-25` (substitute the image
+YAML for other versions):
+
+    cekit --descriptor ubi10-openjdk-25.yaml build podman
+
+This will produce an image named `ubi10/openjdk-25`.
+
+## Contributing
+
+We welcome contributions! For patches, a Developer Certificate of Origin
+(DCO) is required. See [CONTRIBUTING.md](CONTRIBUTING.md).
+
+## License
+
+© 2026 Red Hat, Inc. Distributed under the terms of the Apache License,
+Version 2.0. See [LICENSE](LICENSE) file.