Merge pull request #190 from Yelp/release-s390x-instructions

Add s390x build to release instructions

CONTRIBUTING.md

@@ -31,9 +31,14 @@ The process to release a new version is:
 6. Wait for Travis to run, then find and download the binary and Debian
    packages for both amd64 and ppc64el; there will be links printed at the end
    of the Travis output. Put these into your `dist` directory.
-7. Run `make release`
-8. Run `twine upload --skip-existing dist/*.tar.gz dist/*.whl` to upload the
+7. Wait for the s390x build to run on [OSU OSL's ibmz-ci
+   Jenkins server](https://ibmz-ci.osuosl.org/job/dumb-init/). This should
+   happen automatically within 5 minutes of pushing and produce two artifacts
+   (a binary and a Debian package). Download these into your `dist` directory,
+   similar to the artifacts from Travis.
+8. Run `make release`
+9. Run `twine upload --skip-existing dist/*.tar.gz dist/*.whl` to upload the
    new version to PyPI
-9. Upload the resulting Debian package, binary (inside the `dist` directory),
-   and sha256sums file to a new [GitHub
-   release](https://github.com/Yelp/dumb-init/releases)
+10. Upload the resulting Debian packages, binaries, and sha256sums file (all
+    inside the `dist` directory) to a new [GitHub
+    release](https://github.com/Yelp/dumb-init/releases)