feat: Add blog post with Zephyr 3.0 prep.

docs/blog/2022-03-08-zephyr-3-0-upgrade-prep.md

@@ -0,0 +1,29 @@
+---
+title: "Zephyr 3.0 Update Preparation"
+author: Pete Johanson
+author_title: Project Creator
+author_url: https://gitlab.com/petejohanson
+author_image_url: https://www.gravatar.com/avatar/2001ceff7e9dc753cf96fcb2e6f41110
+tags: [firmware, zephyr, core]
+---
+
+As preparation for completing the [work](https://github.com/zmkfirmware/zmk/pull/1143) to upgrade ZMK to [Zephyr 3.0](https://docs.zephyrproject.org/3.0.0/releases/release-notes-3.0.html), users with user config repositories who wish to avoid future build failures with their GitHub Actions workflows can take steps to adjust
+their repositories now.
+
+GitHub Actions needs to use our latest Docker image to ensure continued compatibility with the ZMK codebase on Zephyr 3.0 (and beyond). You should:
+
+- Open `.github/workflows/build.yml` in your editor/IDE
+- Change `zmkfirmware/zmk-build-arm:2.5` to `zmkfirmware/zmk-build-arm:stable` wherever it is found
+
+Once the changes are committed and pushed, the build will run as expected.
+
+A future blog post will outline the complete Zephyr 3.0 changes once that work is finalized.
+
+:::note
+
+If you created your user config repository a while ago, you may find that your `build.yml` file instead references
+a `zephyr-west-action-arm` custom GitHub Action instead. In this case, the upgrade is not as direct. We suggest that
+instead you [re-create your config repository](/docs/user-setup) to get an updated setup using the new automation
+approach.
+
+:::