Remove unused /var/lib/registry data

docs/partitions.md

@@ -0,0 +1,17 @@
+## config
+The first partition (vfat).
+```
+/opt/monok8s/config        # Config for starting up the cluster, flags, upgrade state, node identity
+```
+
+## Rootfs A/B (readonly)
+OS partition for A/B deployment
+
+
+## data
+```
+/data/
+├── var/                   # mounted to /var
+├── var/lib/registry       # overlay to upperdir for /var/lib/registry
+└── etc-upper/             # optional split if you want control
+```