feat: add initial README with game overview, features, and build instructions

Author: AhmedAmrNabil

README.md

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+# Arena Rush
+
+Arena Rush is a first-person 3D arena shooter built from scratch using C++ and OpenGL, following an Entity-Component-System (ECS) architecture. The player is dropped into a closed urban arena and must survive increasingly difficult waves of enemies while managing limited health and ammunition.
+
+## Features
+
+### Enemies
+
+The game features three distinct enemy archetypes:
+
+- **Brute (Monster)**: A slow, heavily-armoured melee enemy that deals devastating close-range damage.
+- **Charger**: A fast, aggressive melee enemy that rushes the player at high speed.
+- **Drone (Flyer)**: A ranged flying enemy that orbits the player and fires projectiles from a distance.
+
+### Arsenal
+
+The player has access to three switchable weapons:
+
+- **Automatic Rifle (AR)**: Fully automatic, high rate of fire, moderate damage.
+- **Hunting Rifle**: Semi-automatic, very high damage per shot, slow fire rate.
+- **Deagle**: Semi-automatic pistol, balanced damage and fire rate.
+
+### Technical Highlights
+
+- **Graphics & Rendering**: PBR and Blinn Phong shading, Bloom post-processing, HDR tone-mapping, and a blood-splatter screen effect. Full model loading with multiple meshes, materials, and textures.
+- **Animation**: Skeletal animation for all enemy and map models (GLTF).
+- **Physics**: Bullet-physics-based collision with capsule colliders and GImpact & BVH Triangles mesh colliders.
+- **Artificial Intelligence**: Context-steering AI for ground enemies and orbital AI for flyers.
+- **Gameplay Systems**: A data-driven, JSONC-configured wave progression system with 10 escalating waves.
+- **Audio**: Spatial audio via OpenAL (ambient, weapon fire, enemy attacks, reload).
+- **User Interface**: Menu system (Main, Pause, GameOver) with HUD elements including health bar, ammo counter, weapon icon, wave countdown, crosshair, and enemy health bars.
+- **Movement Mechanics**: Sprinting, crouching, sliding, dashing, and jumping with full collision response.
+
+## Getting Started
+
+This project uses `CMake` and `just` (a command runner) for its build system, with optional support for `Nix`.
+
+### Build Commands (using `just`)
+
+- **`just dev`**: Enter the Nix development environment (if using Nix).
+- **`just build`**: Configure and build the project using CMake and Ninja.
+- **`just run`**: Run the game using a dedicated Nvidia/AMD GPU.
+- **`just run-int`**: Run the game on the integrated GPU.
+- **`just clean`**: Remove the `build` and `bin` directories.
+- **`just package`**: Package the project using Nix.
+- **`just desktop`**: Create a desktop entry for the game.
+
+Alternatively, you can manually build using CMake:
+
+```sh
+cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Debug
+cmake --build build
+./bin/ArenaRush
+```