Updating data indexes

[rchan26]

Whenever we want to update our data indexes (perhaps there's new data / updates in the repos that we pull from), we need to rebuild the full index which can be expensive and time-consuming. It would be good to figure out what's been updated and what to add.

We have done this before in this notebook manually, but note this is loading in data from files rather than GitHub readers which we use now.

[rchan26]

See https://docs.llamaindex.ai/en/stable/core_modules/data_modules/index/document_management.html#update