[FIX] mass_mailing: fix mailing model notes

Rewords and fix the typos in the mailing.mailing model notes.

Task-3240405

closes odoo/odoo#116756

X-original-commit: 156b901292b01e6bb6cd430caade3ae95742782b
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/mass_mailing/models/mailing.py

@@ -26,8 +26,7 @@ image_re = re.compile(r"data:(image/[A-Za-z]+);base64,(.*)")
 
 
 class MassMailing(models.Model):
-    """ MassMailing models a wave of emails for a mass mailign campaign.
-    A mass mailing is an occurence of sending emails. """
+    """ Mass Mailing models the sending of emails to a list of recipients for a mass mailing campaign."""
     _name = 'mailing.mailing'
     _description = 'Mass Mailing'
     _inherit = ['mail.thread',