docs: added docstring to parse_xml module

pipeline/beam_etl/helpers/parse_xml.py

@@ -1,3 +1,13 @@
+"""Helper functions to parse the the raw_specifications xml string into a
+dictionary containing the values we are interested in.
+I decided to parse raw_speficications instead of using the "specifications"
+column because the raw data seemed to be cleaner and more consistent, even if
+it requires more effort to parse.
+
+First I parse the xml into a dictionary. Then, I standardize the found keys into
+some keys I expect.
+"""
+
 import logging
 import xml.etree.ElementTree as ET