docs: Add a note for NixOS and containerd

Add a note to remove LimitNOFILE setting in containerd service configuration.

This setting causes multiple issues such as slow `ceph status` commands (and failing healthchecks),
various timeouts, and mons failing/timing out.

Upstream containerd already removed the setting. NixOS hasn't incorporated the change.

This note can be removed once NixOS/nixpkgs#313507 makes it to a stable release.

Signed-off-by: Onur Cakmak <occ@occ.me>

Documentation/Getting-Started/Prerequisites/prerequisites.md

@@ -129,3 +129,11 @@ ConfigMap found in operator.yaml:
 * `CSI_CEPHFS_PLUGIN_VOLUME_MOUNT`
 * `CSI_RBD_PLUGIN_VOLUME`
 * `CSI_RBD_PLUGIN_VOLUME_MOUNT`
+
+If using containerd, remove `LimitNOFILE` from containerd service config to avoid issues like slow ceph commands or mons falling out of quorum.
+
+```nix
+systemd.services.containerd.serviceConfig = {
+ LimitNOFILE = lib.mkForce null;
+};
+```