Update SWY docs to accompany new report

[megannissel]

The following updates need to be made to support the release of a SWY report:

• Add the HTML report to the list of outputs in the "Interpreting Results" section
• Add the new CSV containing monthly average quickflow, baseflow, and precipitation values to the "Interpreting Results" section
• Update units and creation conditions for multiple model outputs

With the introduction of this new output CSV, we may also want to adjust or relax our guidelines surrounding interpreting quickflow and baseflow results; per @newtpatrol on Slack:

I do think it's a good idea to provide it as an additional model output, and it will need to be clearly documented how the baseflow values were calculated. If we're providing this kind of quantified baseflow+quickflow result, then perhaps we should back down on our wording in the UG about baseflow values being interpreted as relative instead of absolute?

Related InVEST PR