Rename census_income_prediction.ipynb to getting_started_notebook.ipynb [(#2115)](GoogleCloudPlatform/python-docs-samples#2115)

renaming the notebooks as Getting Started (will be in sync with the doc). It will be great if the folder could be renamed too

Author: merla18

samples/tables/notebooks/census_income_prediction/census_income_prediction.ipynb renamed to samples/tables/notebooks/census_income_prediction/getting_started_notebook.ipynb

@@ -929,4 +929,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 1
-}
+}