Update README.md

Requirement on the torchvision variant was not documented.

The OCI image tag can not have +, so it was attempted in vain.

Author: kohtala

.github/workflows/main.yml

@@ -62,7 +62,7 @@ jobs:
       # Tags have limited set of valid character, '+' not included
       # https://github.com/opencontainers/distribution-spec/blob/main/spec.md#pulling-manifests
       run: |
-        echo "tag=$(echo -n "${{ matrix.torch }}${{ matrix.index && format('+{0}', matrix.index) || '' }}-${{ matrix.python }}" | tr -c 'a-zA-Z0-9._-' '[-*]')" >> $GITHUB_OUTPUT
+        echo "tag=$(echo -n "${{ matrix.torch }}${{ matrix.index && format('-{0}', matrix.index) || '' }}-${{ matrix.python }}" | tr -c 'a-zA-Z0-9._-' '[-*]')" >> $GITHUB_OUTPUT
 
     - uses: docker/build-push-action@263435318d21b8e681c14492fe198d362a7d2c83 # v6.18.0
       with:

README.md

@@ -16,6 +16,11 @@ packages. To know the packages already installed, run
 
 The output can be used as content of `--constraint` file to `pip-compile`.
 
+The torch builds for +cuNNN are installed from package index
+<https://download.pytorch.org/whl/cuNNN/>. This same index needs to be used to
+install `torchvision`. It is not included in the image because it is fairly
+small and has dependencies we rather maintain in the images build on this.
+
 # License
 
 The image build is licensed using BSD-3, but the underlying Debian, Python,