🙄 misc: Add requirements.txt to make RTD happy

I set up the project using Pipenv, but ReadTheDocs needs a
`requirements.txt` to install the dependencies. It wouldn't be an issue
normally, except I have the Markdown tables extension installed. It is
not installed on RTD VMs by default.

Anyways, docs should build and publish after this commit.

Signed-off-by: Justin W. Flory <git@jwf.io>

Author: justwheel

requirements.txt

@@ -0,0 +1,30 @@
+-i https://pypi.org/simple
+alabaster==0.7.12
+babel==2.8.0
+certifi==2019.11.28
+chardet==3.0.4
+commonmark==0.9.1
+docutils==0.16
+idna==2.9
+imagesize==1.2.0
+jinja2==2.11.1
+markdown==3.0.1
+markupsafe==1.1.1
+packaging==20.3
+pygments==2.6.1
+pyparsing==2.4.6
+pytz==2019.3
+recommonmark==0.6.0
+requests==2.23.0
+six==1.14.0
+snowballstemmer==2.0.0
+sphinx-markdown-tables==0.0.12
+sphinx-rtd-theme==0.4.3
+sphinx==2.4.4
+sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-devhelp==1.0.2
+sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-jsmath==1.0.1
+sphinxcontrib-qthelp==1.0.3
+sphinxcontrib-serializinghtml==1.1.4
+urllib3==1.25.8