docs: move --health-start-interval to unimplemented run flags list

Per review feedback, unimplemented flags belong in the dedicated
unimplemented section rather than inline with implemented flags.

Signed-off-by: Istvan Csaba Varga <istvan-csaba.varga@outlook.com>

Author: IstvanCsVarga

docs/command-reference.md

@@ -343,7 +343,6 @@ Health check flags:
 - :whale: `--health-timeout`: Time to wait before considering the check failed (e.g., 5s)
 - :whale: `--health-retries`: Number of failures before container is considered unhealthy
 - :whale: `--health-start-period`: Start period for the container to initialize before starting health-retries countdown
-- :whale: `--health-start-interval`: Interval between checks during the start period (unimplemented, see [`healthchecks.md`](./healthchecks.md))
 - :whale: `--no-healthcheck`: Disable any health checks defined by image or CLI
 
 Logging flags:
@@ -454,7 +453,8 @@ IPFS flags:
 
 Unimplemented `docker run` flags:
     `--device-cgroup-rule`, `--disable-content-trust`, `--expose`,
-    `--link*`, `--publish-all`, `--storage-opt`, `--volume-driver`
+    `--health-start-interval`, `--link*`, `--publish-all`, `--storage-opt`,
+    `--volume-driver`
 
 ### :whale: nerdctl exec