Is it possible to add help text to addressfield module fields?
When editing the field settings there should be a Help text field where you can enter "Instructions to present to the user below this field on the editing form".

If you want to provide additional instructions, use the Markup module to add a "field" containing the additional instructions. To keep the address field and the markup field in the same fieldset, use the Field group module to group the two fields into a single fieldset group.