wiki: Add some floating window documentation

wiki/Floating-Windows.md

@@ -0,0 +1,16 @@
+### Overview
+
+<sup>Since: next release</sup>
+
+Floating windows in niri always show on top of the tiled windows.
+The floating layout does not scroll.
+Each workspace/monitor has its own floating layout, just like each workspace/monitor has its own tiling layout.
+
+New windows will automatically float if they have a parent (e.g. dialogs) or if they are fixed size (e.g. splash screens).
+To change a window between floating and tiling, you can use the `toggle-window-floating` bind or right click while dragging/moving the window.
+You can also use the `open-floating true/false` window rule to either force a window to open as floating, or to disable the automatic floating logic.
+
+Use `switch-focus-between-floating-and-tiling` to switch the focus between the two layouts.
+When focused on the floating layout, binds (like `focus-column-right`) will operate on the floating window.
+
+You can precisely position a floating window with a command like `niri msg action move-floating-window -x 100 -y 200`.

wiki/_Sidebar.md

@@ -2,6 +2,7 @@
 * [Getting Started](./Getting-Started.md)
 * [Example systemd Setup](./Example-systemd-Setup.md)
 * [Important Software](./Important-Software.md)
+* [Floating Windows](./Floating-Windows.md)
 * [Layer‐Shell Components](./Layer%E2%80%90Shell-Components.md)
 * [IPC, `niri msg`](./IPC.md)
 * [Application-Specific Issues](./Application-Issues.md)