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

tldr/xkill

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# xkill
+
+> Kill a window interactively in a graphical session.
+> See also: `kill`, `killall`.
+> More information: <https://www.x.org/releases/current/doc/man/man1/xkill.1.xhtml>.
+
+- Display a cursor to kill a window when pressing the left mouse button (press any other mouse button to cancel):
+
+`xkill`
+
+- Display a cursor to select a window to kill by pressing any mouse button:
+
+`xkill -button any`
+
+- Kill a window with a specific id (use `xwininfo` to get info about windows):
+
+`xkill -id {{id}}`