Describe what --health-interval does in docker-smoke on current Docker (closes #132)

The old comment said the flag stops the image's 30-second interval from
delaying the first probe past the wait. From Docker 25 on, the first
probe runs 5 seconds after start either way; the flag makes probes
after the 10-second start period come every second instead of every
30. Only the comment changes; TODO.md is left alone because the issue
limits the change to this script.

Model: opus-5-5

script/docker-smoke

@@ -16,8 +16,10 @@ main() {
     # removed on exit.
     key="$(head -c 32 /dev/urandom | base64)"
 
-    # --health-interval=1s overrides the image's 30s interval so the
+    # Docker 25 and later probe every 5 seconds during the image's
-    # first probe does not use up the whole wait.
+    # 10-second start period. --health-interval=1s makes it probe every
+    # second after that instead of every 30, so a slow start still shows
+    # as healthy within the 30-second wait.
     cid="$(docker create --health-interval=1s \
         -e PIXA_SIGNING_KEY="$key" "$("$SCRIPT_DIR/projectname")")"
     # Remove the container on any exit; turning signals into exit makes