Update cheatsheets

linux/xtrlock

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+---
+syntax: markdown
+tags: [tldr, linux]
+source: https://github.com/tldr-pages/tldr.git
+---
+# xtrlock
+
+> Lock the X display until the user supplies their password.
+> More information: <https://manned.org/xtrlock>.
+
+- Lock the display and show a padlock instead of the cursor:
+
+`xtrlock`
+
+- Display a blank screen as well as the padlock cursor:
+
+`xtrlock -b`
+
+- Fork the xtrlock process and return immediately:
+
+`xtrlock -f`