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

tldr/ybacklight

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# ybacklight
+
+> Manage screen backlight brightness. See also `xbacklight`.
+> More information: <https://github.com/pixelcmtd/ybacklight>.
+
+- Print current brightness and maximal brightness, shortened and separated by a slash:
+
+`ybacklight Sc/Sm`
+
+- Specify the brightness:
+
+`ybacklight s{{420}}`
+
+- Increase the brightness by 42 big steps (4200 by default):
+
+`ybacklight Si42`
+
+- Decrease the brightness by 300:
+
+`ybacklight d300`