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

tldr/linux/at

@@ -0,0 +1,25 @@
+---
+syntax: markdown
+tags: [tldr, linux]
+source: https://github.com/tldr-pages/tldr.git
+---
+# at
+
+> Executes commands at a specified time.
+> More information: <https://man.archlinux.org/man/at.1>.
+
+- Open an `at` prompt to create a new set of scheduled commands, press `Ctrl + D` to save and exit:
+
+`at {{hh:mm}}`
+
+- Execute the commands and email the result using a local mailing program such as Sendmail:
+
+`at {{hh:mm}} -m`
+
+- Execute a script at the given time:
+
+`at {{hh:mm}} -f {{path/to/file}}`
+
+- Display a system notification at 11pm on February 18th:
+
+`echo "notify-send '{{Wake up!}}'" | at {{11pm}} {{Feb 18}}`