Update cheatsheets

tldr/linux/showkey

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+---
+syntax: markdown
+tags: [tldr, linux]
+source: https://github.com/tldr-pages/tldr.git
+---
+# showkey
+
+> Display the keycode of pressed keys on the keyboard, helpful for debugging keyboard-related issues and key remapping.
+> More information: <https://manned.org/showkey>.
+
+- View keycodes in decimal:
+
+`sudo showkey`
+
+- Display [s]cancodes in hexadecimal:
+
+`sudo showkey {{-s|--scancodes}}`
+
+- Display [k]eycodes in decimal (default):
+
+`sudo showkey {{-k|--keycodes}}`
+
+- Display keycodes in [a]SCII, decimal, and hexadecimal:
+
+`sudo showkey {{-a|--ascii}}`
+
+- Exit the program:
+
+`Ctrl + d`