Extending output checking guidance to make requests easier to review

Below are some behaviours that make output checking more difficult that we should discourage in the docs.

• Incomplete context. Some of the context descriptions I see only make sense if you have prior knowledge about the project. We should extend this list or context requirements to make it clear that the context should make the request understandable to someone not familiar with the project

• Not using file groups. Some requests group all files into a single group and then write describe groups of files within a single, long context. As a reviewer, this means I have to describe what subset of files i'm referring to when I make any comments. If the files were appropriately grouped in the first place, this would be obvious.

• Producing wide tables that don't have to be wide. Wide tables where all of the columns don't fit into view are difficult to review. Sometimes this is unavoidable, but there are times where it's not necessary. For example:

  	count_numerator_age_18_39	count_denominator_age_18_39	count_numerator_age_40_59	count_denominator_age_40_59	count_numerator_age_60_plus	count_denominator_age_60_plus	count_numerator_sex_F	count_denominator_sex_F	count_numerator_sex_M	count_denominator_sex_M	count_numerator_imd_1	count_denominator_imd_1	count_numerator_imd_5	count_denominator_imd_5
  value	120	1000	340	2500	510	3000	480	3200	490	3300	95	800	140	900

  This is easier to check (visually, and with the built-in summary stats) if it's structured like:

  demographic	category	count_numerator	count_denominator
  age	18–39	120	1000
  age	40–59	340	2500
  age	60+	510	3000
  sex	F	480	3200
  sex	M	490	3300
  imd	1	95	800
  imd	5	140	900

Start with the linked requesting-file-release page and read the “Context and controls” section. Update the guidance to cover understandable context, appropriate file groups, and avoiding unnecessarily wide tables, using the examples in the issue; done means reviewers can find all three recommendations in the documentation.