btrfs-subvolume: add page (#5153)

pages/linux/btrfs-subvolume.md

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+# btrfs subvolume
+
+> Manage btrfs subvolumes and snapshots.
+> More information: <https://btrfs.wiki.kernel.org/index.php/Manpage/btrfs-subvolume>.
+
+- Create a new empty subvolume:
+
+`sudo btrfs subvolume create {{path/to/new_subvolume}}`
+
+- List all subvolumes and snapshots in the specified filesystem:
+
+`sudo btrfs subvolume list {{path/to/btrfs_filesystem}}`
+
+- Delete a subvolume:
+
+`sudo btrfs subvolume delete {{path/to/subvolume}}`
+
+- Create a read-only snapshot of an existing subvolume:
+
+`sudo btrfs subvolume snapshot -r {{path/to/source_subvolume}} {{path/to/target}}`
+
+- Create a read-write snapshot of an existing subvolume:
+
+`sudo btrfs subvolume snapshot {{path/to/source_subvolume}} {{path/to/target}}`
+
+- Show detailed information about a subvolume:
+
+`sudo btrfs subvolume show {{path/to/subvolume}}`