Add extra/optional Markdown dependency to setup.py

- Modify documentation to use the extra dependency in order to install
the recommended markdown package version.

1 files changed, 3 insertions, 0 deletions

diff --git a/setup.py b/setup.py
index 5eea85b6..0979d1c4 100755
--- a/setup.py
+++ b/setup.py
@@ -61,6 +61,9 @@ setup(
                           for name in names],
     },
     install_requires=requires,
+    extras_require={
+        'Markdown': ['markdown~=3.1.1']
+    },
     entry_points=entry_points,
     classifiers=[
         'Development Status :: 5 - Production/Stable',