Add LICENSE file to zip

(cherry picked from commit 5905b37)

Author: sanak

pb_tool.cfg

@@ -24,7 +24,7 @@ compiled_ui_files:
 resource_files: resources.qrc
 
 # Other files required for the plugin
-extras: metadata.txt icon.png
+extras: metadata.txt icon.png LICENSE
 
 # Other directories to be deployed with the plugin.
 # These must be subdirectories under the plugin directory