Docs: Add configuration file for read the docs (#670)

Documentation builds on read the docs are currently failing. The
documentation build is trying to install all required pip packages for
development. It fails for one C-package that needs compilation.

The documentation build does not need all these packages. The
configuration can be changed in the admin panel of read the docs or
with a configuration file. A configuration file is the recommended way.

This commit introduces a basic configuration file for the read the docs
documentation build.

Author: jensvog

.readthedocs.yml

@@ -0,0 +1,10 @@
+# .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: docs/conf.py