steam: add page (#5736)

pages/common/steam.md

@@ -0,0 +1,24 @@
+# steam
+
+> Video game platform by Valve.
+> More information: <https://developer.valvesoftware.com/wiki/Command_Line_Options#Steam_.28Windows.29>.
+
+- Launch Steam, printing debug messages to stdout:
+
+`steam`
+
+- Launch Steam and enable its in-app debug console tab:
+
+`steam -console`
+
+- Log into Steam with the specified credentials:
+
+`steam -login {{username}} {{password}}`
+
+- Launch Steam in Big Picture Mode:
+
+`steam -tenfoot`
+
+- Exit Steam:
+
+`steam -shutdown`