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

tldr/linux/systemd-nspawn

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+---
+syntax: markdown
+tags: [tldr, linux]
+source: https://github.com/tldr-pages/tldr.git
+---
+# systemd-nspawn
+
+> Spawn a command or OS in a lightweight container.
+> More information: <https://www.freedesktop.org/software/systemd/man/latest/systemd-nspawn.html>.
+
+- Run a command in a container:
+
+`systemd-nspawn --directory {{path/to/container_root}}`
+
+- Run a full Linux-based OS in a container:
+
+`systemd-nspawn --boot --directory {{path/to/container_root}}`
+
+- Run the specified command as PID 2 in the container (as opposed to PID 1) using a stub init process:
+
+`systemd-nspawn --directory {{path/to/container_root}} --as-pid2`
+
+- Specify the machine name and hostname:
+
+`systemd-nspawn --machine={{container_name}} --hostname={{container_host}} --directory {{path/to/container_root}}`