docs: add CONTRIBUTING.md and CII best-practices criteria helper

The scripts/cii_criteria.py helper fetches bestpractices.dev criteria
and generates pre-filled edit URLs for each criterion, streamlining
badge maintenance. CONTRIBUTING.md backs the contribution and testing
criteria referenced by the CII best-practices submission.

CONTRIBUTING.md

@@ -0,0 +1,40 @@
+# Contributing to MT5-Quant
+
+Thanks for your interest in improving MT5-Quant! This document explains how to
+contribute and what we expect from contributions.
+
+## How to contribute
+
+1. **Fork** the repository and create a topic branch from `master`.
+2. Make your change, keeping it focused (one logical change per PR).
+3. Open a **pull request against `master`**. A pull request template
+   (`.github/PULL_REQUEST_TEMPLATE.md`) is provided — please fill it in.
+4. Ensure CI passes (build, `cargo test`, clippy, formatting, cargo-deny,
+   CodeQL). Maintainers review and merge once checks and review are satisfied.
+
+## Development setup
+
+- Install Rust (stable toolchain) and, for full backtests, Wine/MT5 as described
+  in `README.md` and `docs/QUICKSTART.md`.
+- Build the release binary with either:
+  - `bash scripts/build-rust.sh`, or
+  - `cargo build --release`
+- The binary is produced at `target/release/mt5-quant`.
+
+## Testing requirement
+
+- **Non-trivial changes must include tests.** New functionality should come with
+  unit or integration tests where practical.
+- `cargo test` runs automatically in CI (`rust.yml`) on every push and pull
+  request, so a change that breaks tests cannot merge.
+
+## Commit style
+
+- Follow **Conventional Commits** (`feat:`, `fix:`, `docs:`, `refactor:`,
+  `test:`, `release:`), as documented in `AGENTS.md`.
+
+## Issue tracker
+
+- Bugs and enhancement requests are tracked on the project's
+  [GitHub Issues](https://github.com/masdevid/mt5-quant/issues), with
+  bug-report and feature-request templates under `.github/ISSUE_TEMPLATE/`.