add topic description

Author: linhard

Schemas/markup.xsd

@@ -70,6 +70,7 @@
 			<xs:element name="CreationDate" type="xs:dateTime" minOccurs="0"/>
 			<xs:element name="ModifiedDate" type="xs:dateTime" minOccurs="0"/>
 			<xs:element name="AssignedTo" type="UserIdType" minOccurs="0" maxOccurs="1"/>
+			<xs:element name="Description" type="xs:string" minOccurs="0" maxOccurs="1"/>
 			<xs:element name="BimSnippet" type="BimSnippet" minOccurs="0" maxOccurs="1"/>
 			<!-- Name of the file in the topic folder or url -->
 			<xs:element name="DocumentReference" minOccurs="0" maxOccurs="unbounded">