Add development guide for local QuickFIX/Go work

DEVELOPMENT_GUIDE.md

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+# QuickFIX/Go – Development guide
+
+This document provides a short, practical checklist for working on QuickFIX/Go during local development. It complements the main `README.md` and `CONTRIBUTING.md`.
+
+## 1. Prerequisites
+
+- Go toolchain (Go 1.21+ is recommended, see the main README for current requirements)
+- `make`
+- Optional but recommended:
+  - Docker and VS Code if you want to use the devcontainer setup described in CONTRIBUTING
+
+Verify your Go installation:
+
+~~~bash
+go version
+~~~
+
+## 2. Running unit tests
+
+To run the standard Go test suite:
+
+~~~bash
+go test ./...
+~~~
+
+This should pass before you open a pull request.
+
+If you want to focus on a specific package:
+
+~~~bash
+go test ./config
+go test ./store
+~~~
+
+## 3. Acceptance tests overview
+
+QuickFIX/Go ships with a comprehensive acceptance test suite shared across QuickFIX implementations. Running these tests is slower, but very useful when touching protocol-level behaviour.
+
+Typical flow (see the main README and CONTRIBUTING for full details):
+
+~~~bash
+# Generate FIX code from specs
+make generate
+
+# Build the acceptance test server
+make build-test-srv
+
+# Run acceptance tests
+make accept
+~~~
+
+Acceptance tests require Ruby to be available in `PATH`. If you are using the provided devcontainer, Ruby is already installed.
+
+## 4. Suggested workflow for contributors
+
+1. Ensure Go and `make` are installed.
+2. Make your code changes.
+3. Run fast feedback:
+   - `go test ./...`
+4. For protocol-sensitive changes, also run:
+   - `make generate`
+   - `make build-test-srv`
+   - `make accept`
+5. Format your code using the standard Go tooling:
+   - `go fmt ./...`
+6. Commit with a clear message and open a pull request describing:
+   - What you changed
+   - Why it is useful for QuickFIX/Go users
+   - Which test commands you ran locally