Improve "Configuring your Mail Server" document

According to Crowd 3.3 Release Notes:

Multiple server alert addresses
From now on, Crowd lets you configure multiple server alert email addresses, so whenever some alert occur, every of these emails receive notification.

(which relates to CWD-5018)

However, the document Configuring your Mail Server still mentions Server alert email as a field that could only receive one e-mail address. The screenshot must also be updated.

It is also unclear about how should the e-mail addresses be separated in the field (comma, semi-colon, etc).