docs: add CONTRIBUTING.md with Windows setup instructions

CONTRIBUTING.md

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+# Contributing to HeatWatch
+
+Thank you for your interest in improving HeatWatch! This guide will help you get the development environment running on your machine.
+
+---
+
+## Quick Start (macOS / Linux)
+
+```bash
+git clone https://github.com/castroquiles/HeatWatch.git
+cd HeatWatch
+
+python -m venv venv
+source venv/bin/activate
+
+pip install -e ".[dev]"
+
+pytest
+```
+
+---
+
+## Windows Setup
+
+This section covers Windows-specific steps and common gotchas.
+
+### Prerequisites
+
+* **Python 3.10+** — Download from [python.org](https://www.python.org/downloads/). During installation, check **“Add Python to PATH”**.
+* **Git** — Download from [git-scm.com](https://git-scm.com/download/win).
+* **GDAL / rasterio dependencies** — These can be tricky on Windows. The easiest route is using **conda**.
+
+### Step 1: Install Miniconda
+
+1. Download Miniconda from [https://docs.conda.io/en/latest/miniconda.html](https://docs.conda.io/en/latest/miniconda.html)
+2. Run the installer and accept the defaults
+3. Open **Anaconda Prompt** (or Windows Terminal with PowerShell)
+
+### Step 2: Create and activate a conda environment
+
+```powershell
+conda create -n heatwatch python=3.11
+conda activate heatwatch
+```
+
+> **Gotcha:** If `conda activate heatwatch` fails with “CommandNotFoundError”, run:
+> ```powershell
+> conda init powershell
+> ```
+> Then **restart your terminal**.
+
+### Step 3: Install GDAL and spatial libraries
+
+```powershell
+conda install -c conda-forge gdal rasterio fiona shapely pyproj
+```
+
+> **Gotcha:** Do **not** use `pip install rasterio` on Windows without first installing GDAL via conda. You will get missing DLL errors.
+
+### Step 4: Clone and install HeatWatch
+
+```powershell
+git clone https://github.com/castroquiles/HeatWatch.git
+cd HeatWatch
+
+pip install -e ".[dev]"
+```
+
+### Step 5: Verify the installation
+
+```powershell
+pytest
+heatwatch --help
+```
+
+If both commands run without errors, you're ready to contribute!
+
+---
+
+## Common Windows Gotchas
+
+| Problem | Cause | Solution |
+|---------|-------|----------|
+| `ImportError: DLL load failed` | GDAL not installed or not on PATH | Install GDAL via `conda install -c conda-forge gdal` |
+| `conda activate` does nothing | Shell not initialized for conda | Run `conda init powershell` and restart terminal |
+| `pip install rasterio` fails | Missing C++ build tools / GDAL headers | Use `conda install -c conda-forge rasterio` instead |
+| Long path errors during clone | Windows default path limit (260 chars) | Enable long paths: `git config --global core.longpaths true` |
+| Slow test execution | Anti-virus scanning Python bytecode | Add your project folder to AV exclusions temporarily |
+
+---
+
+## Submitting Changes
+
+1. **Fork** the repository
+2. **Create a branch**: `git checkout -b feat/your-feature-name`
+3. **Make your changes** and add tests if applicable
+4. **Run tests**: `pytest`
+5. **Commit**: `git commit -m "feat: describe your change"`
+6. **Push**: `git push origin feat/your-feature-name`
+7. **Open a Pull Request** against `main`
+
+---
+
+## Code Style
+
+* Follow PEP 8
+* Use meaningful variable names
+* Add docstrings to public functions
+* Keep functions small and focused
+
+---
+
+## Need Help?
+
+* Open an [Issue](https://github.com/castroquiles/HeatWatch/issues)
+* Start a [Discussion](https://github.com/castroquiles/HeatWatch/discussions)
+* Comment on the issue you're working on