docs for contributors

CONTRIBUTING.md

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+# Contributing
+
+## Developers installation
+
+Install dependencies
+
+```python
+pip install -U pip setuptools
+pip install "numpy<2"
+pip install -r requirements.txt -e .
+```
+
+Start the main application
+
+```python
+pymca
+```
+
+or using the module directly
+
+```python
+python -m PyMca5.PyMcaGui.pymca.PyMcaMain
+```
+
+## Deployment
+
+TODO