Mislabeled function in "Running Parts of an Experiment" docs section

The [Running Parts of an Experiment](https://dssg.github.io/triage/experiments/running/#running-parts-of-an-experiment) section of the Triage documentation references calling `experiment.generate_imputed_features() `. However in the [base.py](https://github.com/dssg/triage/blob/master/src/triage/experiments/base.py) file, the function is renamed to `impute_missing_features`.

Open the “Running Parts of an Experiment” section in the linked Triage documentation and compare its function reference with src/triage/experiments/base.py. Update the documentation to use impute_missing_features instead of generate_imputed_features, then verify the rendered text no longer names the old function.

Written by the indexing model from the issue text.