Add basic root documentation using rustdoc

src/main.rs

@@ -1,3 +1,46 @@
+//! Payphone is a Discord bot that allows users to make calls to each other, similar to a phone
+//! system.
+//! 
+//! # Setting Up
+//! 
+//! First of all, clone the Git repository and navigate to the project directory:
+//! 
+//! ```shell
+//! $ git clone --branch rewrite https://git.nyeki.dev/payphone/payphone.git
+//! $ cd payphone
+//! ```
+//! 
+//! To boot up Payphone, you'll need both a Discord bot token and  a Scylla database cluster with
+//! at least 3 nodes.
+//! 
+//! - To get a Discord bot token, create a new bot application on the
+//!   [Discord Developer Portal](https://discord.com/developers/applications).
+//! 
+//! - To set up a Scylla database cluster, make sure to have Docker and Docker Compose installed
+//!   and run `docker compose up -d`. A development cluster will be created with 3 nodes, with one
+//!   of them listening at `127.0.0.1:9042`.
+//! 
+//! To stop the database cluster at any time, run `docker compose down`. To stop it and delete the
+//! volumes (resetting the database), run `docker compose down -v`.
+//! 
+//! # Booting Up
+//! 
+//! Payphone has a CLI interface that allows you to pass the bot token and database URL as CLI
+//! arguments. To get all possible arguments, run the following command:
+//! 
+//! ```shell
+//! $ cargo run -- --help
+//! ```
+//! 
+//! Payphone also supports configuration via environment variables and `.env` files by default.
+//! 
+//! ```env
+//! PAYPHONE_TOKEN="your_discord_bot_token"
+//! ```
+//! 
+//! All environment variables are prefixed with `PAYPHONE_` and can be used to override the CLI
+//! arguments.
+
 use clap::Parser;
 use twilight_gateway::Intents;