docs: drop dir suggestion from artifact-type=docker note

Source-dir fingerprinting only works as an end-to-end identity if the
runtime side also fingerprints the source dir. Standard Kosli runtime
reporters fingerprint the running image, so suggesting dir as a generic
swap is misleading — the attested and running artifacts would never
link. Push and oci are the safe answers for the typical case.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: AlexKantor87

cmd/kosli/root.go

@@ -52,8 +52,7 @@ Note: ^--artifact-type=docker^ reads the image's repo digest via the local Docke
 The image must have been pushed to or pulled from a registry for a repo digest to exist;
 a freshly built image (just ^docker build^) will not have one. If the image is already in
 a registry, prefer ^--artifact-type=oci^, which fetches the digest directly from the
-registry without needing a local Docker daemon. To fingerprint the source instead, use
-^--artifact-type=dir^ on the build context.
+registry without needing a local Docker daemon.
 
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