message: Update README for s390x Stable release.
  Updated README for s390x Stable release.
diff: @@ -117,6 +117,7 @@ The TensorFlow project strives to abide by generally accepted best practices in
  Build Type | Status | Artifacts
  --------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------
  **Linux s390x Nightly** | [![Build Status](http://ibmz-ci.osuosl.org/job/TensorFlow_IBMZ_CI/badge/icon)](http://ibmz-ci.osuosl.org/job/TensorFlow_IBMZ_CI/) | [Nightly](http://ibmz-ci.osuosl.org/job/TensorFlow_IBMZ_CI/)
  +**Linux s390x CPU** Stable Release | [![Build Status](http://ibmz-ci.osuosl.org/job/TensorFlow_IBMZ_Release_Build/badge/icon)](https://ibmz-ci.osuosl.org/job/TensorFlow_IBMZ_Release_Build/) | [Release](https://ibmz-ci.osuosl.org/job/TensorFlow_IBMZ_Release_Build/)
  **Linux ppc64le CPU** Nightly | [![Build Status](https://powerci.osuosl.org/job/TensorFlow_PPC64LE_CPU_Build/badge/icon)](https://powerci.osuosl.org/job/TensorFlow_PPC64LE_CPU_Build/) | [Nightly](https://powerci.osuosl.org/job/TensorFlow_PPC64LE_CPU_Nightly_Artifact/)
  **Linux ppc64le CPU** Stable Release | [![Build Status](https://powerci.osuosl.org/job/TensorFlow_PPC64LE_CPU_Release_Build/badge/icon)](https://powerci.osuosl.org/job/TensorFlow_PPC64LE_CPU_Release_Build/) | [Release](https://powerci.osuosl.org/job/TensorFlow_PPC64LE_CPU_Release_Build/)
  **Linux ppc64le GPU** Nightly | [![Build Status](https://powerci.osuosl.org/job/TensorFlow_PPC64LE_GPU_Build/badge/icon)](https://powerci.osuosl.org/job/TensorFlow_PPC64LE_GPU_Build/) | [Nightly](https://powerci.osuosl.org/job/TensorFlow_PPC64LE_GPU_Nightly_Artifact/)
  