docs: add README with quick start and docs links

Co-Authored-By: Virgil <virgil@lethean.io>

README.md

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+# go-ratelimit
+
+Provider-agnostic sliding window rate limiter for LLM API calls. Enforces requests per minute (RPM), tokens per minute (TPM), and requests per day (RPD) quotas per model using an in-memory sliding window. Ships with default quota profiles for Gemini, OpenAI, Anthropic, and a local inference provider. State persists across process restarts via YAML (single-process) or SQLite (multi-process, WAL mode). Includes a Gemini-specific token counting helper and a YAML-to-SQLite migration path.
+
+**Module**: `forge.lthn.ai/core/go-ratelimit`
+**Licence**: EUPL-1.2
+**Language**: Go 1.25
+
+## Quick Start
+
+```go
+import "forge.lthn.ai/core/go-ratelimit"
+
+// YAML backend (default, single-process)
+rl, err := ratelimit.New()
+
+// SQLite backend (multi-process)
+rl, err := ratelimit.NewWithSQLite("~/.core/ratelimits.db")
+defer rl.Close()
+
+ok, reason := rl.CanSend("gemini-2.0-flash", 1500)
+if ok {
+    rl.RecordUsage("gemini-2.0-flash", 1500)
+}
+```
+
+## Documentation
+
+- [Architecture](docs/architecture.md) — sliding window algorithm, provider quotas, YAML and SQLite backends
+- [Development Guide](docs/development.md) — prerequisites, test patterns, coding standards
+- [Project History](docs/history.md) — completed phases with commit hashes, known limitations
+
+## Build & Test
+
+```bash
+go test ./...
+go test -race ./...
+go vet ./...
+go build ./...
+```
+
+## Licence
+
+European Union Public Licence 1.2 — see [LICENCE](LICENCE) for details.