Readthedocs (#1555)

* add readthedocs config file for sphinx-copy button

.readthedocs.yml

@@ -0,0 +1,17 @@
+---
+# .readthedocs.yaml
+# 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: docs/conf.py
+
+# Optionally Python version and requirements required to build your docs
+python:
+   version: 3.9
+   install:
+      - requirements: docs/requirements.txt

docs/requirements.txt

@@ -0,0 +1,3 @@
+Sphinx==3.5.4
+sphinx-copybutton==0.3.1
+sphinx_rtd_theme==0.5.2