Merge branch 'rtd-docs' into 'master'

Integrate docs to XFEL RTD

See merge request !99

.readthedocs.yml

+# .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: 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
\ No newline at end of file

doc/requirements.txt

+sphinx
+sphinx_rtd_theme
+autoapi
+sphinx-autoapi
\ No newline at end of file