refactor doc

docs/mkdocs/src/development/python_environments.md

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+PYTHON ENVIRONMENTS
+===================
+
+When you don't want to install Bumble in your main/default python environment, 
+using a virtual environment, where the package and its dependencies can be
+installed, isolated from the rest, may be useful.
+
+There are many flavors of python environments and dependency managers. 
+This page describes a few of the most common ones.
+
+
+## venv
+
+`venv` is a standard module that is included with python.
+Visit the [`venv` documentation](https://docs.python.org/3/library/venv.html) page for details.
+
+## Pyenv
+
+`pyenv` lets you easily switch between multiple versions of Python. It's simple, unobtrusive, and follows the UNIX tradition of single-purpose tools that do one thing well.  
+Visit the [`pyenv` site](https://github.com/pyenv/pyenv) for instructions on how to install
+and use `pyenv`
+
+## Conda
+
+Conda is a convenient package manager and virtual environment.
+The file `environment.yml` is a Conda environment file that you can use to create
+a new Conda environment. Once created, you can simply activate this environment when
+working with Bumble.  
+Visit the [Conda site](https://docs.conda.io/en/latest/) for instructions on how to install
+and use Conda.
+A few useful commands:  
+
+### Create a new `bumble` Conda environment
+```
+$ conda env create -f environment.yml
+```
+This will create a new environment, named `bumble`, which you can then activate with:
+```
+$ conda activate bumble
+```
+
+### Update an existing `bumble` environment
+```
+$ conda env update -f environment.yml
+```