KNOWN_ISSUES: add CephFS bug description

See #1160

Author: vrutkovs

KNOWN_ISSUES.md

@@ -8,3 +8,8 @@
   **Workaround:** Start installation with a pull secret from cloud.redhat.com, enable new source in operatorhub settings.
 
   OKD-specific catalog with community versions of mentioned operators is in progress.
+
+## [CephFS mounts get invalid permissions](https://github.com/openshift/okd/issues/1160)
+  **Effected Versions:** 4.10.0-0.okd-2022-03-07-131213
+  **Description:** Due to kernel 4.16 bug CephFS mounts get invalid permissions, so writing to image registry backed by CephFS fails on OKD 4.10
+  **Workaround**: In `ceph-csi-cephfs` installation add `wsync` to `kernelMountOptions`