[FIX] Development readme

README-dev.md

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+Orange development
+==================
+
+The source code of [Orange] is versioned in [Git] and hosted on [GitHub]. 
+If you want to contribute to this open-source project you will have to use git. However, for minor experimentation with the source code you can also get by without. 
+
+[Orange]: https://orange.biolab.si/
+[Git]: https://git-scm.com/
+[GitHub]: https://github.com/biolab/orange
+
+Prerequisites
+-------------
+
+[Orange] is written mostly in Python, therefore you'll need [Python 3] version 3.6 or newer.
+
+You will also need a C/C++ compiler. On Windows, you can get one by installing [Visual Studio].
+A slightly more "minimalistic" option is to install only its [Build Tools].
+
+[Python 3]: https://www.python.org
+[Visual Studio]: https://visualstudio.microsoft.com/vs/
+[Build Tools]: https://visualstudio.microsoft.com/visual-cpp-build-tools/
+
+Source code
+-----------
+
+Get the source code by cloning the git repository
+
+    git clone https://github.com/biolab/orange3.git
+
+or, alternatively, download and unpack the [ZIP archive] of the source code from [GitHub].
+
+[ZIP archive]: https://github.com/biolab/orange3/archive/master.zip
+
+Building
+--------
+
+Consider using virtual environments to avoid package conflicts. 
+
+Install the required Python packages
+
+    pip install -r requirements.txt
+
+and run the setup script with a development option, which will link to the source code instead of creating a new package in Python's site-packages.
+
+    python setup.py develop
+
+Verify the installation by importing the Orange package from Python and loading an example Iris dataset.
+
+    >>> import Orange
+    >>> print(Orange.data.Table("iris")[0])
+    [5.1, 3.5, 1.4, 0.2 | Iris-setosa]
+
+Using the graphic user interface requires some additional packages
+
+    pip install -r requirements-gui.txt
+
+and Qt dependencies.
+
+    pip install PyQt5 PyQtWebEngine
+
+To start Orange GUI from the command line, run:
+
+    python3 -m Orange.canvas
+
+Contributing
+------------
+
+If you've made improvements that you want to contribute, you'll need your own fork of the [GitHub] repository. After committing and pushing changes to your fork, you can create a pull request. We will review your contribution and hopefully merge it after any potential corrections. 
+
+You can view the list of open [pull requests] and known [issues] on GitHub.
+
+[pull requests]: https://github.com/biolab/orange3/pulls
+[issues]: https://github.com/biolab/orange3/issues