Configuring: add Environment variables page

Co-authored-by: NotAShelf <itsashelf@gmail.com>
Co-authored-by: Antonino Scordino <a.scordino.07@gmail.com>
Co-authored-by: vaxerski <43317083+vaxerski@users.noreply.github.com>

pages/Configuring/Environment-variables.md

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+As  [previously mentioned](../Getting-Started/Quick-start/#wrapping-the-launcher-recommended), it's 
+useful using a wrapper to launch Hyprland. Whether you start Hyprland through TTY or a Display 
+Manager, it is always suggested to use one. As such, you can pass certain environment 
+variables to improve Wayland compatibility, or simply change certain aspects of your desktop.
+
+Please avoid putting those environment variables in /etc/environment. That will cause all
+sessions (including Xorg ones) to pick up your wayland-specific environment on traditional
+Linux distros.
+
+# XDG Specifications
+
+- `XDG_CURRENT_DESKTOP=Hyprland`
+- `XDG_SESSION_TYPE=wayland`
+- `XDG_SESSION_DESKTOP=Hyprland`
+
+XDG specific environment variables are often detected through portals and applications that may
+set those for you, however it is a good idea to provide them in your wrapper script as a fail-safe.
+
+# QT Variables
+
+- `QT_AUTO_SCREEN_SCALE_FACTOR=1` - [(From the QT documentation)](https://doc.qt.io/qt-5/highdpi.html)
+enables automatic scaling, based on the monitor's pixel density
+- `QT_QPA_PLATFORM="wayland;xcb"` - Tell QT applications to use the Wayland backend, and fall back to x11 if Wayland is unavailable
+- `QT_WAYLAND_DISABLE_WINDOWDECORATION=1` - Disables window decorations on QT applications
+- `QT_QPA_PLATFORMTHEME=qt5ct` - Tells QT based applications to pick your theme from qt5ct, use with Kvantum.
+
+# NVIDIA Specific
+
+To force GBM as a backend, set the following environment variables:
+
+- `GBM_BACKEND=nvidia-drm`
+- `__GLX_VENDOR_LIBRARY_NAME=nvidia`
+
+> See [Archwiki Wayland Page](https://wiki.archlinux.org/title/Wayland#Requirements) for more details on those variables.
+
+- `LIBVA_DRIVER_NAME=nvidia` - Hardware acceleration on NVIDIA GPUs
+
+> See [Archwiki Hardware Acecleration Page](https://wiki.archlinux.org/title/Hardware_video_acceleration)
+> for details and necessary values before setting this variable.
+
+- `__GLX_GSYNC_ALLOWED` - Controls if G-Sync capable monitors should use Variable Refresh Rate (VRR)
+
+> See [Nvidia Documentation](https://download.nvidia.com/XFree86/Linux-32bit-ARM/375.26/README/openglenvvariables.html) for details.
+
+- `__GL_VRR_ALLOWED` - Controls if Adaptive Sync should be used. Recommended to set as "0" to avoid having problems on some games.
+
+- `WLR_DRM_NO_ATOMIC=1` - use legacy DRM interface instead of atomic mode setting. Might fix flickering issues.
+
+# Toolkit Backend Variables
+
+- `SDL_VIDEODRIVER=wayland` - Run SDL2 applications on Wayland. Remove or set to x11 if games that provide older versions of SDL cause
+  compatibility issues
+- `_JAVA_AWT_WM_NONEREPARENTING=1` - Fix possibly broken Java applications. Set to 1 until Wakefield is available.
+- `CLUTTER_BACKEND="wayland"` - Clutter package already has wayland enabled, this variable will force Clutter applications
+  to try and use the Wayland backend
+
+- `GDK_BACKEND` - Force backend for wayland-enabled GTK3 and GTK4 backends. Available options are "wayland" or "x11". If GTK XWayland
+  applications cause issues when set to "wayland", try "wayland,x11"
+
+# Theming Related Variables
+
+- `GTK_THEME` - Set a GTK theme manually, for those who want to avoid appearance tools lxappearance or nwg-look
+- `XCURSOR_THEME` - Set your cursor theme. The theme needs to be installed and readable by your user.
+- `XCURSOR_SIZE` - Set cursor size. See [here](../FAQ/) for why you might want this variable set.