Mcaliley review: better description of what n-day flow means

In single_gage_n_day_flows_analysis.ipynb:

• As a non-specialist, I wasn't sure what the first sentence ("Demonstration of use of hywsap python package for analyzing different n-day flows for a single streamgage") meant by "n-day flows." Maybe there's different language that could say the same thing without the sort of jargony "n-days"? Something like "analyzing flows averaged with different time window lengths"? This perspective is incredibly valuable because we want this package to be accessible to many different levels of expertise. We have added text in the notebook about what we mean by n-day flows, and changed the heading to refer to "streamflow N-day Averages" rather than "N-day streamflows". Hopefully this helps to clarify the workflow.