Update CONTRIBUTING.md

Author: sidneymbell

CONTRIBUTING.md

@@ -9,3 +9,15 @@ Note that baltic follows and enforces the [Contributor Covenant Code of Conduct]
 If you'd like to contribute a bug fix feel free to start a pull request outlining the problem and its solution.
 For adding code for a new tree manipulation function or for a novel visualisation please open an issue first and describe the goal and suggested approach first.
 Even if suggested manipulations/visualisations don't make it into baltic's code base (_e.g._ if the application isn't broad) there will be room to share it under examples.
+
+#### Release process  
+Notes for internal use:  
+1. Make a new github tag following [semantic versioning](https://medium.com/the-non-traditional-developer/semantic-versioning-for-dummies-45c7fe04a1f8)  
+2. Edit the [version number](https://github.com/evogytis/baltic/blob/master/setup.py#L11) and [download url](https://github.com/evogytis/baltic/blob/master/setup.py#L14) in `setup.py`  
+3. Push to pypi
+
+```
+pip install twine  
+python3 setup.py sdist 
+twine upload dist/*
+```