Update requirements.txt according to the recommendations for libraries:

Dependencies are specified in the setup.py,
and could be resolved from here.
See:
https://pip.pypa.io/en/stable/user_guide/#requirements-files
and https://caremad.io/posts/2013/07/setup-vs-requirement/

requirements.txt

@@ -1,10 +1 @@
-Click==7.0
-Jinja2==2.11.1
-livereload==2.6.1
-Markdown==3.2.1
-MarkupSafe==1.1.1
-mkdocs==1.0.4
-nose==1.3.7
-PyYAML==5.3
-six==1.14.0
-tornado==6.0.3
+-e .