Document suggestions for users if catch is 0 in fcast and end year

[k-doering-NOAA]

See discussion in nmfs-ost/ss3-source-code#324.

It could be helpful to document solutions users may want to consider if 0 catch in the last year is causing issues in the bmark and forecasting quantities.

[e-perl-NOAA]

@Rick-Methot-NOAA do you think it's still worth providing guidance on this in the user manual?

[Rick-Methot-NOAA]

I think I need to improve the text in forecast.ss_new first. Let's re-open the code issue #324 with intent to clarify controls related to relative F among fleets. Then in the doc we can point to those controls.

[e-perl-NOAA]

@Rick-Methot-NOAA You closed the ss3-source-code issue 324 on September 8, given that it has been closed do you think there is any further text that needs to be added about controls related to relative F among fleets?

[Rick-Methot-NOAA]

I think we need to expand upon the lead-in line for this section of the forecast file. Currently the manual simply has:
"There are 2 options for entering Forecast Years:"
then it proceeds to try to describe option 1.
I will keep this on a lower priority to-do list.

[e-perl-NOAA]

Option 2 is described:

[Rick-Methot-NOAA]

What I think we need to add is a description of the role of forecast years in structuring the model calculations before continuing with the current/modified descriptions of the two options for entering forecast years. I will work on an alternative.