modified: README.md

modified:   docs/desktop-environments/kde.md
renamed:    docs/desktop-environments/xfc4.md -> docs/desktop-environments/xfce4.md
new file:   docs/display-managers/gdm.md
new file:   docs/display-managers/sddm.md
new file:   docs/display-protocols/wayland.md
new file:   docs/display-protocols/x11.md
new file:   docs/window-managers/hyprland.md
new file:   docs/window-managers/kwin.md

docs/display-managers/sddm.md

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+# SSDM (Simple Desktop Display Manager)
+
+SDDM (Simple Desktop Display Manager) is the default graphical login manager used by KDE Plasma. It provides the interface where users log in to their desktop session and switch between user accounts or desktop environments.
+
+**🧩 Key Features:**
+
+- **Qt-based:** Built with the Qt toolkit, making it visually consistent with KDE Plasma.
+- **Wayland and X11 support:** Compatible with both display protocols, aligning with KDE’s transition toward Wayland.
+- **Theming:** Highly customizable with animated and branded login screens.
+- **Session management:** Allows selection of desktop environments and user sessions.
+
+**⚙️ Configuration:**
+
+- **GUI:** Accessible via System Settings → Startup and Shutdown → Login Screen (SDDM).
+- **CLI:** Configurable through /etc/sddm.conf or /etc/sddm.conf.d/.
+
+**🧭 Role in KDE:**
+
+- Replaced KDM (KDE Display Manager) starting with KDE Plasma 5.
+- Used by KDE-centric distributions like KDE neon, OpenSUSE KDE, and Fedora KDE Spin.