name no consumer of this node

A source that documents itself through a specific downstream node depends on
that node to be understood, and that node already depends on this one for
frames. The README pointed at one by name and the CI workflow still carried a
comment about the dataflow that wired it, which no longer exists.

The output is documented by its type instead: wire `image` into anything that
takes std/media/v1/Image. PREVIEW covers seeing the frames without naming
anyone. Generic words like "a viewer" or "a consumer" stay, since they describe
a role rather than a repository.

dora_webcam/image.py

@@ -1,8 +1,8 @@
 """Packing a frame as std/media/v1/Image.
 
-The struct is respelled here rather than imported from the viewer: node
-repositories share no source package, so the manifest and this schema are the
-whole contract between them.
+The struct is respelled here rather than imported: node repositories share no
+source package, so the manifest and this schema are the whole contract a
+consumer has.
 """
 
 import numpy as np