docs: add project README

Author: bilyayeva

README.md

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+# MathPlotter++
+
+![C++20](https://img.shields.io/badge/C%2B%2B-20-00599C?logo=cplusplus)
+![CMake](https://img.shields.io/badge/CMake-3.22%2B-D22128?logo=cmake)
+![Linux](https://img.shields.io/badge/platform-Linux-FCC624?logo=linux&logoColor=black)
+![CI](https://github.com/bilyayeva/math-plotter/actions/workflows/ci.yml/badge.svg)
+![License](https://img.shields.io/badge/license-MIT-3DA639)
+
+Math Plotter++ is an application for plotting mathematical functions, built
+with C++20, [SFML](https://github.com/SFML/SFML) for graphics, [muParser](https://github.com/beltoforion/muparser) for parsing mathematical expressions,
+and [Dear ImGui](https://github.com/ocornut/imgui) for the user interface.
+
+## Features
+
+### Multiple Functions
+
+Plot up to 15 mathematical functions simultaneously.
+
+![Functions](assets/media/functions.png)
+
+### Themes
+
+Switch between three color themes.
+
+![Themes](assets/media/themes.gif)
+
+### Navigation
+
+Pan and zoom using the mouse while the coordinate grid dynamically adapts
+to the current zoom level.
+
+![Zoom](assets/media/zoom.gif)
+
+### Function Customization
+
+Change function colors and get immediate feedback for invalid expressions.
+
+![Customization](assets/media/customization.gif)
+
+## Architecture
+
+Math Plotter++ is split into separate components, each responsible for a
+specific part of the application. The `Application` class manages the main
+application lifecycle and connects these components together.
+
+- `Application`: manages the application lifecycle and coordinates components.
+- `CameraController`: handles graph navigation, zooming, and the viewport.
+- `GridRenderer`: renders the coordinate grid, axes, and labels.
+- `FunctionRenderer`: parses and renders mathematical functions.
+- `UserInterface`: manages the ImGui-based user interface.
+- `Theme`: manages application color themes.
+- `ColorPalette`: defines the colors used by the themes.
+
+## Build and Run
+
+Math Plotter++ currently targets Linux.
+
+### Requirements
+
+- C++20 compatible compiler
+- CMake 3.22 or newer
+- Git
+
+On Ubuntu and other Debian-based distributions, install the required tools
+and SFML system dependencies:
+
+```bash
+sudo apt update
+
+sudo apt install \
+    build-essential \
+    cmake \
+    git \
+    libx11-dev \
+    libxrandr-dev \
+    libxcursor-dev \
+    libxi-dev \
+    libudev-dev \
+    libfreetype-dev \
+    libgl1-mesa-dev \
+    libegl1-mesa-dev
+```
+
+### Build
+
+Clone the repository:
+
+```bash
+git clone https://github.com/<username>/math-plotter.git
+cd math-plotter
+```
+
+Configure and build the project:
+
+```bash
+cmake -S . -B build
+cmake --build build
+```
+
+CMake automatically downloads and builds SFML, Dear ImGui, ImGui-SFML,
+and muParser.
+
+### Run
+
+```bash
+./build/mathplotter
+```
+
+## License
+
+This project is licensed under the terms of the [MIT License](LICENSE).