[doc/tutorial] Update install instructions

Author: mpsonntag

doc/tutorial.rst

@@ -88,20 +88,22 @@ the project name `python-odml <https://github.com/G-Node/python-odml>`_.
 Dependencies
 ------------
 
-The Python-odML library (version 1.4) runs under Python 2.7 or 3.5.
+The Python-odML library (version 1.4+) runs under Python 3.6+.
 
-Additionally, the Python-odML library depends on Enum, lxml, pyyaml and rdflib.
+Additionally, the Python-odML library depends on the lxml, pyyaml and rdflib python packages.
 
 When the odML-Python library is installed via pip or the setup.py, these
 packages will be automatically downloaded and installed. Alternatively, they
 can be installed from the OS package manager.
 
-On Ubuntu, the dependency packages are available as ``python-enum`` and
-``python-lxml``.
+On Ubuntu, the dependency packages are available as ``python-lxml``, ``python-yaml`` and ``python-rdflib``.
 
 Note that on Ubuntu 14.04, the latter package additionally requires the
 installation of ``libxml2-dev``, ``libxslt1-dev``, and ``lib32z1-dev``.
 
+Python 2 has reached end of life. We will not keep any future versions of odml Python 2 compatible and also advertise using a Python version >= 3.6. If a Python version < 3.6 is a requirement, the following dependency needs to be installed as well:
+
+The ``enum34`` package with a ``pip`` installation or ``python-enum`` using the OS package manager.
 
 Installation...
 ---------------
@@ -120,8 +122,8 @@ downloaded and installed.
 If you are not familiar with PyPI and pip, please have a look at the available
 online documentation.
 
-Installation
-------------
+... from source:
+****************
 
 To download the Python-odML library please either use git and clone the
 repository from GitHub::