docs/dev/pinned-coreos.md: update rhcos-stream.json example

The file data/data/rhcos-stream.json was deleted in
openshift@d773ee5
and the corresponding data now lives in data/data/coreos/rhcos.json. Let's update
the documentation to reflect this change.

docs/dev/pinned-coreos.md

@@ -24,7 +24,7 @@ that data into the cluster as well.
 To update the bootimage for one or more architectures, use e.g.
 
 ```
-$ plume cosa2stream --target data/data/rhcos-stream.json --distro rhcos  x86_64=48.83.202102230316-0 s390x=47.83.202102090311-0 ppc64le=47.83.202102091015-0 --url https://rhcos-redirector.apps.art.xq1c.p1.openshiftapps.com/art/storage/releases --no-signatures
+$ plume cosa2stream --target data/data/coreos/rhcos.json --distro rhcos  x86_64=48.83.202102230316-0 s390x=47.83.202102090311-0 ppc64le=47.83.202102091015-0 --url https://rhcos-redirector.apps.art.xq1c.p1.openshiftapps.com/art/storage/releases --no-signatures
 ```
 
 For more information on this command, see:
@@ -39,3 +39,4 @@ For historical reference, the initial file `data/data/rhcos-stream.json` was gen
 ```
 $ plume cosa2stream --name rhcos-4.8 --distro rhcos  x86_64=48.83.202102230316-0 s390x=47.83.202102090311-0 ppc64le=47.83.202102091015-0 > data/data/rhcos-stream.json
 ```
+NOTE: the data for `data/data/rhcos-stream.json` now lives in `data/data/coreos/rhcos.json`