Document verified OTBR IPv6 startup script

apps/matter-server/README.md

@@ -21,8 +21,10 @@ this is recovery with preserved state, not uninterrupted active-active service.
 The MikroTik-managed `app-otbr` container requires these startup sysctls in
 its own network namespace: `net.ipv6.conf.all.forwarding=1`,
 `net.ipv6.conf.veth-app-otbr.accept_ra=2`, and
-`net.ipv6.conf.veth-app-otbr.accept_ra_from_local=1`. Its container entrypoint
-applies them before `/init`. Without accepting its own router advertisements,
+`net.ipv6.conf.veth-app-otbr.accept_ra_from_local=1`. The persistent script
+`/data/lan-ipv6-init.sh` applies them before `exec /init`; the RouterOS container
+uses `entrypoint=/bin/sh` and `cmd=/data/lan-ipv6-init.sh`. Keeping the script
+separate avoids RouterOS command-line quoting errors. Without accepting its own router advertisements,
 the container advertises a LAN prefix but lacks the corresponding return
 route; discovery works while IPv6 communication with Thread fails. Recheck
 this entrypoint after changing or reinstalling the MikroTik App. RouterOS