linstor: patches README describes ForceInitialSyncPermanent as backup-only #4886

The entry for snapshot-restore-drbd-initialized.diff in packages/system/linstor/images/piraeus-server/patches/README.md reads as if DrbdOptions/ForceInitialSyncPermanent only comes from a backup. The code is described correctly, the wording is just too narrow.

At the backported upstream commit 9d8cdf511 the property is set in three places: CtrlBackupCreateApiCallHandler for a backup, MixedStorPoolHelper for mixed storage pools, and CtrlRscCrtApiHelper.copyForceInitialSyncProp when DrbdOptions/ForceInitialSync is true at resource creation. All three take the path that recreates metadata. The entry should name the backup as an example, not as the only source. Review thread: #4866 (comment)