Move to dedicated md

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

TROUBLESHOOTING.md

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+# Troubleshooting
+
+## Errors on pushing to registry
+
+While pushing to a registry, you may encounter these kinds of issues:
+
+* `failed commit on ref "layer-sha256:...": invalid content digest in response: invalid checksum digest format`
+* `failed commit on ref "layer-sha256:...": no response`
+* `failed commit on ref "manifest-sha256:...": unexpected status: 401 Unauthorized`
+* `unexpected response: 401 Unauthorized`
+
+These issues are not directly related to this action but are rather linked to [buildx](https://github.com/docker/buildx),
+[buildkit](https://github.com/moby/buildkit), [containerd](https://github.com/containerd/containerd) or the registry
+on which you're pushing your image. The quality of error message depends on the registry and are usually not very informative.
+
+To help you solve this, you should first enable debugging in the
+[setup-buildx action step](https://github.com/docker/setup-buildx-action):
+
+```yaml
+  -
+    name: Set up Docker Buildx
+    uses: docker/setup-buildx-action@v1
+    with:
+      buildkitd-flags: --debug
+```
+
+Next you can test pushing with containerd using [this workflow](https://github.com/crazy-max/ghaction-setup-containerd#build-and-push-docker-image).
+Do not forget to set `ctr --debug` for the pushing step. If it works then open an issue on
+[buildkit](https://github.com/moby/buildkit) repository.