A couple of small changes.

python_prep_guidelines.md

@@ -37,6 +37,7 @@ Python that you can learn but won't be relevant for this course.
         - Selecting rows with conditions
     - Grouping and aggregating dataframes
     - Obtaining statistics from columns
+    - Creating new columns through operations on existing columns
 - Seaborn
     - Understaning seaborn plots
     - How to plot data from a pandas dataframe with seaborn
@@ -47,9 +48,11 @@ Python that you can learn but won't be relevant for this course.
   notebook: https://colab.research.google.com/?utm_source=scs-index
 - A more detailed, high quality example Colab
   notebook: https://colab.research.google.com/github/cs231n/cs231n.github.io/blob/master/python-colab.ipynb
-- https://www.youtube.com/watch?v=8VFYs3Ot_aA
-- https://www.youtube.com/watch?v=oCngVVBSsmA
-- A short, 4 hours intro to Python from
+- A brief video intro to Colab (
+  Spanish): https://www.youtube.com/watch?v=8VFYs3Ot_aA
+- Another brief video intro to Colab (
+  English): https://www.youtube.com/watch?v=oCngVVBSsmA
+- A free, 4 hours intro to Python from
   Datacamp: https://www.datacamp.com/courses/intro-to-python-for-data-science
 - A self-pace introduction to Python for STEM
   applications: https://www.pythonlikeyoumeanit.com/index.html