docs: fix quickstart rig-core imports

[Parikalp-Bhardwaj]

Summary

This PR fixes the Rig quickstart setup so the install command matches the imports used in the example.

The docs currently install rig-core, but the example imports from rig. Since the example is written using the public rig crate path, the install command should install rig instead.

Problem

The quickstart currently shows:

cargo add rig-core tokio

But the example uses:

use rig::client::{CompletionClient, ProviderClient};
use rig::completion::Prompt;
use rig::providers::openai;

This can confuse new users because installing rig-core directly would require importing from rig_core, while the documented example imports from rig.

The example also uses:

#[tokio::main]
async fn main() -> Result<(), anyhow::Error>

So the setup should include Tokio with the required runtime features and the anyhow dependency.

Changes

Updated the install command from:

cargo add rig-core tokio

to:

cargo add rig anyhow dotenvy
cargo add tokio --features macros,rt-multi-thread

This keeps the example imports unchanged:

use rig::client::{CompletionClient, ProviderClient};
use rig::completion::Prompt;
use rig::providers::openai;

Also added:

dotenvy::dotenv().ok();

before creating the OpenAI client, so users can load OPENAI_API_KEY from a local .env file during development.

Why

This makes the quickstart easier to follow and copy-paste for new users.

With the updated install command, users get:

• rig for the documented import path
• tokio with the async runtime features required for #[tokio::main]
• anyhow for the example error type
• dotenvy to load OPENAI_API_KEY from a local .env file during development

dotenvy is useful because many users prefer to store API keys in a .env file instead of exporting them manually in the terminal. This lets the quickstart work with:

OPENAI_API_KEY=your-api-key

Then the example can load it with:

dotenvy::dotenv().ok();

[linear-code]

RIG-1327