add crane exampleg

README.md

@@ -7,7 +7,7 @@ It fails if both images provide the same platforms, or if either isn't a manifes
 # demo
 
 ```
-go run ./ \
+$ go run ./ \
     gcr.io/distroless/static:nonroot \
     mcr.microsoft.com/windows/nanoserver:1809 \
     gcr.io/imjasonh/combined
@@ -15,5 +15,41 @@ go run ./ \
 
 This combines the [distroless](https://github.com/googlecontainertools/distroless) image providing linux platform support with an image providing Windows support.
 
+You can check the image's platforms using [`crane`](https://github.com/google/go-containerregistry/blob/main/cmd/crane/README.md):
+
+```
+$ crane manifest gcr.io/imjasonh/combined | jq '.manifests[].platform'
+{
+  "architecture": "amd64",
+  "os": "linux"
+}
+{
+  "architecture": "arm",
+  "os": "linux"
+}
+{
+  "architecture": "arm64",
+  "os": "linux"
+}
+{
+  "architecture": "ppc64le",
+  "os": "linux"
+}
+{
+  "architecture": "s390x",
+  "os": "linux"
+}
+{
+  "architecture": "amd64",
+  "os": "windows",
+  "os.version": "10.0.17763.1935"
+}
+{
+  "architecture": "arm",
+  "os": "windows",
+  "os.version": "10.0.17763.1935"
+}
+```
+
 The result is an image that provides support for both.
 This image is intended to be suitable as a base image used with `ko` to provide multi-arch _and multi-OS_ support for a Go application.