Update cheatsheets

tldr/linux/systemctl-cat

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+---
+syntax: markdown
+tags: [tldr, linux]
+source: https://github.com/tldr-pages/tldr.git
+---
+# systemctl cat
+
+> Show the full contents of unit files as systemd sees them.
+> More information: <https://www.freedesktop.org/software/systemd/man/latest/systemctl.html#cat%20PATTERN%E2%80%A6>.
+
+- Show the contents and absolute path of a unit file:
+
+`systemctl cat {{unit}}`
+
+- Show the contents of multiple unit files:
+
+`systemctl cat {{unit1 unit2 ...}}`
+
+- Show the contents of a unit file for a template:
+
+`systemctl cat {{template@}}`