Add btrfs snapshot cleanup procedure.

README.md

@@ -52,3 +52,12 @@ Post-Install - Secrets Setup
 - mkdir -p ~/.config/sops/age
 - age-keygen -o ~/.config/sops/age/keys.txt
 - nixverse secrets edit
+
+Maintenance - Clean Up BTRFS old_roots
+
+- sudo mkdir /mnt
+- sudo mount /dev/mapper/cryptroot -o subvolid=5 /mnt
+- cd /mnt/old_roots
+- sudo du -h -d 1
+- sudo rm -rf [snapshot here]
+