[CI:DOCS] Minor update to podmanimage upstream docs
Add a reference to where/how podman is compiled for the 'upstream'
flavored image.
@@ -32,7 +32,9 @@ The container images are:
* `quay.io/podman/upstream:latest` - This image is built daily using the latest
code found in this GitHub repository. Due to the image changing frequently,
it's not guaranteed to be stable or even executable. The image is built with
- [the upstream Containerfile](upstream/Containerfile).
+ [the upstream Containerfile](upstream/Containerfile). Note the actual compilation
+ of upstream podman [occurs continuously in
+ COPR](https://copr.fedorainfracloud.org/coprs/rhcontainerbot/podman-next/).
## Sample Usage
