[FIX] Add Python requirements file for RTD build

.readthedocs.yaml

@@ -18,3 +18,8 @@ sphinx:
 # 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: docs/source/requirements.txt

docs/source/requirements.txt

@@ -0,0 +1 @@
+myst_parser