making graphviz optional (#24)

Author: rafaelfsilva

docs/source/quickstart_installation.rst

@@ -4,34 +4,6 @@ Installation
 WfCommons is available on `PyPI <https://pypi.org/project/wfcommons>`_.
 WfCommons requires Python3.6+ and has been tested on Linux and macOS.
 
-Requirements
-------------
-
-Graphviz
-^^^^^^^^
-
-WfCommons uses `pygraphviz <https://pygraphviz.github.io/documentation/latest/install.html>`_
-and thus needs the `graphviz <https://www.graphviz.org/>`_ package installed (version 2.16
-or later). You can install graphviz easily on Linux with your favorite package manager,
-for example for Debian-based distributions:
-
-.. code-block:: bash
-
-    $ sudo apt-get install graphviz libgraphviz-dev
-
-and for RedHat-based distributions:
-
-.. code-block:: bash
-
-    $ sudo yum install python-devel graphviz-devel
-
-On macOS you can use the :code:`brew` package manager:
-
-.. code-block:: bash
-
-    $ brew install graphviz
-
-
 Installation using pip
 ----------------------
 
@@ -55,3 +27,31 @@ repository: ::
     $ git clone https://github.com/wfcommons/wfcommons
     $ cd wfcommons
     $ pip install .
+
+Optional Requirements
+---------------------
+
+Graphviz
+^^^^^^^^
+
+WfCommons uses `pygraphviz <https://pygraphviz.github.io/documentation/latest/install.html>`_
+for generating visualizations for the workflow task graph . If you want to enable this 
+feature, you will have to install the `graphviz <https://www.graphviz.org/>`_ package (version 2.16
+or later). You can install graphviz easily on Linux with your favorite package manager,
+for example for Debian-based distributions:
+
+.. code-block:: bash
+
+    $ sudo apt-get install graphviz libgraphviz-dev
+
+and for RedHat-based distributions:
+
+.. code-block:: bash
+
+    $ sudo yum install python-devel graphviz-devel
+
+On macOS you can use the :code:`brew` package manager:
+
+.. code-block:: bash
+
+    $ brew install graphviz

setup.py

@@ -33,7 +33,6 @@
         'matplotlib',
         'networkx',
         'numpy',
-        'pygraphviz',
         'python-dateutil',
         'requests',
         'scipy',