Update cheatsheets

tldr/linux/bcachefs-device

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+---
+syntax: markdown
+tags: [tldr, linux]
+source: https://github.com/tldr-pages/tldr.git
+---
+# bcachefs device
+
+> Manage devices within a running `bcachefs` filesystem.
+> More information: <https://bcachefs-docs.readthedocs.io/en/latest/mgmt-devicemanagement.html>.
+
+- Format and add a new device to an existing filesystem.:
+
+`sudo bcachefs device add --label={{group}}.{{name}} {{path/to/mountpoint}} {{path/to/device}}`
+
+- Migrate data off a device to prepare for removal:
+
+`bcachefs device evacuate {{path/to/device}}`
+
+- Permanently remove a device from a filesystem:
+
+`bcachefs device remove {{path/to/device}}`