title: Add Multiselect dropdown in Odoo module
body: <p>I want to add a multiselect dropdown in Odoo module 
  Field name will be Weekly Holiday which will be use to select multiple days of week</p>
  
  <p>Below python is code i tried.
  'weeklyholiday': fields.selection([('Sunday', 'Sunday'), ('Monday', 'Monday'), ('Tuesday', 'Tuesday'),('Wednesday', 'Wednesday'),], "Weekly Holiday"),</p>