[Keymap] Add brauner preonic layout (#19444)

keyboards/preonic/keymaps/brauner/readme.md

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+# Brauner's Preonic Keymap
+
+This is a keymap layout heavily optimized for vim.
+It mostly follows `QWERTY` but moves various symbols on to different layers.
+
+* Number keys function only as number keys.
+  Additional symbols they would produce when `Shift` is held are turned off as they are intercepted.
+* `Y`, `P`, and `X` function as `Ctrl+C`, `Ctrl+V`, and `Ctrl+X` when held.
+  This avoids having to hold down `Ctrl` and also aligns regular copy and paste with vim functionality.
+* Various keys perform different functions when tapped than when held.
+* `!` and `?` are on top of `.` on different layers.
+* `\` and `|` are on top of `/` on different layers.
+* `:` and `;` are on top of `,` on different layers.
+* All navigation is done via `H`, `J`, `K`, and `L`.
+* `O`, `U`, `S`, and `A` produce the Umlauts `Ö`, `Ü`, `ß`, and `Ä` when held.
+  This relies on the operating system keyboard layout to be set to US Intl.
+* Different layers will activate different types of navigation.
+  For example, left, right, up, and down or backspace, page up, page down, and tab.
+* There's a dedicated mouse layer which can be activated allowing to navigate solely with the keyboard where otherwise a mouse or trackpad would be needed.
+* There's a dedicated management layer where the boot loader can be entered or music mode can be turned on or off.
+* Lastly, there's a compositor layer which is optimized for managing a tiling window manager.
+  The layer is used specifically via layer-mod keys in the base layer.
+  In other words, specific modifiers are held when this layer is accessed.
+* Opening and closing brackets are always located on adjacent keys on the same layer.
+  Pressing a matching opening and closing bracket key at the same time will insert both brackets and move the cursor into the middle of the bracket pair.
+  As should be obvious, this is useful when programming: `(|)`, `[|]`, `{|}`, `<|>`.