Provide Examples of Additions in EAD4

[alexduryee]

From the Chicago meeting - there's a lot of confusion around how to describe additions to collections in EAD. There are elements that can almost be used to describe them (but not quite), so EAD users are improperly using elements, or have to devise a local method for encoding this information. The EAD BPG should provide clear examples of using elements like <accrurals> and recommendations for how to encode information about additions.