Move pages under tldr, lint run.sh, update docs

tldr/linux/btrfs-filesystem

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+---
+syntax: markdown
+tags: [tldr, linux]
+source: https://github.com/tldr-pages/tldr.git
+---
+# btrfs filesystem
+
+> Manage btrfs filesystems.
+> More information: <https://btrfs.readthedocs.io/en/latest/btrfs-filesystem.html>.
+
+- Show filesystem usage (optionally run as root to show detailed information):
+
+`btrfs filesystem usage {{path/to/btrfs_mount}}`
+
+- Show usage by individual devices:
+
+`sudo btrfs filesystem show {{path/to/btrfs_mount}}`
+
+- Defragment a single file on a btrfs filesystem (avoid while a deduplication agent is running):
+
+`sudo btrfs filesystem defragment -v {{path/to/file}}`
+
+- Defragment a directory recursively (does not cross subvolume boundaries):
+
+`sudo btrfs filesystem defragment -v -r {{path/to/directory}}`
+
+- Force syncing unwritten data blocks to disk(s):
+
+`sudo btrfs filesystem sync {{path/to/btrfs_mount}}`
+
+- Summarize disk usage for the files in a directory recursively:
+
+`sudo btrfs filesystem du --summarize {{path/to/directory}}`