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

tldr/steam

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# steam
+
+> Video game platform by Valve.
+> More information: <https://developer.valvesoftware.com/wiki/Command_Line_Options>.
+
+- Launch Steam, printing debug messages to `stdout`:
+
+`steam`
+
+- Launch Steam and enable its in-app debug console tab:
+
+`steam -console`
+
+- Enable and open the Steam console tab in a running Steam instance:
+
+`steam steam://open/console`
+
+- Log into Steam with the specified credentials:
+
+`steam -login {{username}} {{password}}`
+
+- Launch Steam in Big Picture Mode:
+
+`steam -tenfoot`
+
+- Exit Steam:
+
+`steam -shutdown`