Add missing file import

The TemplateCreator.addin-template.xml file was not included in the
generated .mpack

Author: mrward

src/MonoDevelop.TemplateCreator/TemplateCreator.addin.xml

@@ -14,6 +14,7 @@
 		<Import file="MonoDevelop.TemplateCreator.dll" />
 		<Import file="Microsoft.TemplateEngine.Merged.dll" />
 		<Import file="ConfigurationFiles/template.json" />
+		<Import file="TemplateCreator.addin-template.xml" />
 	</Runtime>
 
 	<Dependencies>