Improve plugin description

Author: jajm

plugin.ini

@@ -1,7 +1,7 @@
 [info]
 name = "Element Types"
 author = "Julian Maurice"
-description = "Allow elements to have a type"
+description = "Allow elements to have a type, thus allowing easier input. For instance, this plugin implements the 'date' type and show a datepicker widget for elements of this type. Other types can be implemented by plugins."
 version = "0.1"
 license = "GPLv3"
 link = "https://github.com/biblibre/omeka-plugin-ElementTypes"