Update 02-create_surveys.md

Added instructions for "Matrix" question type.

docs/06-start_here/06-activities/02-create_surveys.md

@@ -45,7 +45,7 @@ When selecting the question type, please note the following:
 - `SHORT ANSWER` questions act exactly like `TEXT` questions, except they have a shorter character limit (about a sentence).
 - `RATING` questions allows the individual to rate their response on a custom like `LIST` questions, except they only display numerical rating options.
 - `TIME` questions prompt the individual with a box in which only text for hours and minutes "HH:MM" is accepted, either in military time or in standard time,
-- `MATRIX` questions allow several survey items to be grouped together in a table with the same set of instructions and answer choices.
+- `MATRIX` questions allow several survey items to be grouped together in a table with the same set of instructions and answer choices. The first survey item can have any question type except for "Matrix", and subsequent survey items must have the "Matrix" question type.
 
 # Delete an Individual Option in Your Question's List of Options: