Update cheatsheets

tldr/linux/pivot_root

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+---
+syntax: markdown
+tags: [tldr, linux]
+source: https://github.com/tldr-pages/tldr.git
+---
+# pivot_root
+
+> Change the root filesystem to a new directory and move the current root to a subdirectory of the new root.
+> Commonly used during system initialization (e.g., in `initramfs`) to switch from a temporary root to the real root filesystem.
+> More information: <https://manned.org/pivot_root.8>.
+
+- Make `/new_root` the new root (`/`) and move current root to a subdirectory of it:
+
+`sudo pivot_root {{path/to/new_root}} {{path/to/new_root/old_root}}`
+
+- Display help:
+
+`pivot_root {{[-h|--help]}}`