documentation: Add readthedocs configuration (#41)

Advantages of using a file instead of the dashboard:
https://docs.readthedocs.io/en/stable/config-file/index.html

Author: speller26

.gitignore

@@ -24,3 +24,4 @@ pip-wheel-metadata/
 /doc/_apidoc/
 /build
 /venv
+/dist

.readthedocs.yml

@@ -0,0 +1,20 @@
+# .readthedocs.yml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+# Build documentation in the docs/ directory with Sphinx
+sphinx:
+  configuration: doc/conf.py
+
+# Optionally build your docs in additional formats such as PDF
+formats:
+  - pdf
+
+# Optionally set the version of Python and requirements required to build your docs
+python:
+  version: 3.7
+  install:
+    - requirements: doc/requirements.txt

doc/requirements.txt

@@ -0,0 +1,2 @@
+sphinx
+sphinx-rtd-theme