added mention of Symbol attribute - v5.0 (#363)

Author: julitafalcondusza

docs/pim/work_with_product_attributes.md

@@ -20,6 +20,7 @@ Available attribute types are:
 - Measurement (range) - measurement with a given unit and minimum/maximum values selectable per product type
 - Measurement (single) - measurement with a single value in given unit
 - Selection - one of a list of customizable options
+- Symbol - value of product's symbol attribute
 
 If the default list of attributes is not sufficient, ask your development team to [create a custom attribute type]([[= developer_doc =]]/pim/create_custom_attribute_type/).