docs: add note about pandas req in Get Started

[rich-iannone]

This adds a note about the requirement for Pandas in the Get Started guide.

Fixes: #529

[machow]

If this shows up as expected in the docs, then LGTM! (I did not look at the preview docs)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.67%. Comparing base (b32b55a) to head (ef8d325).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #559   +/-   ##
=======================================
  Coverage   90.67%   90.67%           
=======================================
  Files          46       46           
  Lines        5381     5381           
=======================================
  Hits         4879     4879           
  Misses        502      502           

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