Use Altair/Vega-Lite instead of Plotly express in Readme.md

Change-Id: I8f22c23715af9944bcf5f4595f0ab07b1a3381fd
diff --git a/figures/hello-world.png b/figures/hello-world.png
index 58579df..031872d 100644
--- a/figures/hello-world.png
+++ b/figures/hello-world.png
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