suppress sphinx spurious warning when auto-generating the API docs

sphinx.errors.SphinxWarning: ../docs/reference/api.md::toctree directive not expected with external-toc [etoc.toctree]

This workaround is suggested here:
executablebooks/sphinx-external-toc#36

Until that bug and executablebooks/sphinx-external-toc#79 are fixed, we need this!

docs/_config.yml

@@ -42,6 +42,8 @@ sphinx:
     - sphinx.ext.autodoc
 
   config:
+    suppress_warnings : ["etoc.toctree"] # Workaround for: https://github.com/executablebooks/sphinx-external-toc/issues/36
+                                         # and: https://github.com/executablebooks/sphinx-external-toc/issues/79
     autodoc_default_options: {
      "members": True,                # Include module/class members.
      "member-order": 'bysource',     # Order members as in source file.