Added a requirements file for 'readthedocs'

The module 'sphinxcontrib.bibtex' could not be loaded

	new file:   .readthedocs.yaml
	new file:   src/sdoc/requirements.txt

Author: hbr

.readthedocs.yaml

@@ -0,0 +1,30 @@
+# .readthedocs.yaml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+# Set the version of Python and other tools you might need
+build:
+  os: ubuntu-20.04
+  tools:
+    python: "3.9"
+    # You can also specify other tool versions:
+    # nodejs: "16"
+    # rust: "1.55"
+    # golang: "1.17"
+
+# Build documentation in the src/sdoc/ directory with Sphinx
+sphinx:
+   configuration: src/sdoc/conf.py
+
+
+# If using Sphinx, optionally build your docs in additional formats such as PDF
+formats:
+    - pdf
+
+# Optionally declare the Python requirements required to build your docs
+python:
+   install:
+   - requirements: src/sdoc/requirements.txt

src/sdoc/requirements.txt

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+sphinxcontrib.bibtex