Add llms.txt for LLM-friendly project documentation

[alexei-led]

Summary

Add an llms.txt file following the llms.txt convention.

Proposed Content

# spotinfo

> CLI tool for AWS EC2 Spot Instance pricing, savings, and interruption frequency data.

spotinfo provides real-time and cached access to AWS Spot Instance data — pricing, savings percentages, interruption rates, and placement scores. It embeds AWS data feeds for offline capability and supports multiple output formats (table, JSON, CSV, text).

## Docs

- [README](https://github.com/alexei-led/spotinfo/blob/master/README.md): Full documentation, installation, usage
- [Development Guide](https://github.com/alexei-led/spotinfo/blob/master/CLAUDE.md): Build, test, architecture details

## Architecture

- **CLI framework:** urfave/cli/v2
- **Data sources:** Spot Advisor JSON (embedded), spot pricing JS (embedded), EC2 DescribeSpotPriceHistory API (live fallback)
- **Core package:** `internal/spot/` — client.go (orchestration), price.go (pricing), liveprice.go (API fallback), score.go (placement), types.go
- **MCP integration:** `internal/mcp/` — MCP server tools and handlers
- **Output formats:** number, text, json, table, csv
- **Build:** Go 1.24+, Makefile-based, multi-platform releases
- **Docker:** Multi-arch (amd64/arm64), scratch-based, ghcr.io

## CLI API

- `spotinfo --type <instance-type>` — Query specific instance type
- `spotinfo --region <region>` — Filter by AWS region
- `spotinfo --os <linux|windows>` — Filter by OS
- `spotinfo --output <format>` — Output format (number/text/json/table/csv)
- `spotinfo --sort <field>` — Sort results
- `spotinfo --min-savings <N>` — Minimum savings percentage filter
- `spotinfo --max-interruption <N>` — Maximum interruption frequency (0-4 scale)

References

• https://llmstxt.org/