Adds custom attribute support for buy-button.js, updated instructions, and compiled libraries

[TaylorTheDeveloper]

• Add custom attributes to product line items during checkout
• Attributes are visible to customers during the checkout process
• Attributes are accessible in the Shopify admin panel and through webhooks as metadata
• Updates instructions to help folks build the project quickly in Linux or wsl environment
• Includes precompiled libraries and references for those that want to learn