Update StandardNamesRules.rst: two identical quantities from different processes that need to be kept apart

[climbfuji]

Description

Update StandardNamesRules.rst: two identical quantities from different processes that need to be kept apart.

I did not update standard_names.xml because the base variable cumulative_change_of_x_wind_due_to_convective_GWD isn't listed yet, and it doesn't make sense to add cumulative_change_of_x_wind_due_to_convective_whole_atmosphere_GWD. We can add both, but then we should add many more such variables, and that is like opening a can of worms.

Questions for the reviewers: Should cumulative_change_of be added, or should we use the existing change_over_time_in instead?

Update: I removed cumulative_change_of from the PR, since it is not directly related to the issue that this PR addresses.

Issues

Closes #79

[mkavulich]

Sorry I didn't get to this sooner. The new rule looks good.

If I am understanding the use case for the new prefix, it is for quantitative changes in value of a variable since some specified point in time? In this case, I'd propose something along the lines of change_in _X_ since _Y, where Y could be previous_timestep, start_of_forecast, etc.

If I'm not understanding the exact use case let me know.

[climbfuji]

Sorry I didn't get to this sooner. The new rule looks good.

If I am understanding the use case for the new prefix, it is for quantitative changes in value of a variable since some specified point in time? In this case, I'd propose something along the lines of change_in _X_ since _Y, where Y could be previous_timestep, start_of_forecast, etc.

If I'm not understanding the exact use case let me know.

That makes sense to me. Let's chat about this tomorrow and get this PR merged before I go on leave next week.

[nusbaume]

Looks good to me, just a couple optional text change requests.

[gold2718]

This is okay with me.