add RTD requirements.txt

.readthedocs.yaml

@@ -30,6 +30,6 @@ sphinx:
 # Optional but recommended, declare the Python requirements required
 # to build your documentation
 # See https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
-# python:
-#    install:
-#    - requirements: docs/requirements.txt
+python:
+   install:
+   - requirements: cli_docs/requirements.txt

cli_docs/conf.py

@@ -24,7 +24,7 @@ release = "0.4.0"
 
 # If your documentation needs a minimal Sphinx version, state it here.
 #
-needs_sphinx = '1.8.5'
+needs_sphinx = '3.5.4'
 
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
@@ -49,13 +49,6 @@ source_suffix = '.rst'
 # The master toctree document.
 master_doc = 'index'
 
-# The language for content autogenerated by Sphinx. Refer to documentation
-# for a list of supported languages.
-#
-# This is also used if you do content translation via gettext catalogs.
-# Usually you set "language" from the command line for these cases.
-language = None
-
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
 # This pattern also affects html_static_path and html_extra_path.

cli_docs/requirements.txt

@@ -0,0 +1,4 @@
+# docs
+sphinx==3.5.4  # newer versions display function names in the wrong color?
+sphinx_rtd_theme==0.5.2
+Jinja2<3.1  # https://github.com/readthedocs/readthedocs.org/issues/9038