dolphin/ppsspp/steam/steam deck: restructured

wiki/games/steam_deck.md

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+# Steam Deck
+
+The [Steam Deck](https://store.steampowered.com/steamdeck) is a handheld gaming
+computer made by the same developers as [Steam](./steam.md).
+Due to its form factor it can be used especially well to play games that need a
+controller, such as many games that run on [emulators](./emulators.md).
+But by adding a USB-hub and connecting keyboard and mouse it can be used to
+play classical PC games aswell.
+
+## Shortcuts
+
+- Esc: `STEAM + D-Pad Left`
+- Show Keyboard: `STEAM + X`