[DOC] mail_reply: when reply button is visible, how-to see sent message (#138)

mail_reply/doc/index.rst

@@ -5,5 +5,14 @@
 Usage
 =====
 
-* Open Discuss menu
-* All messages have reply button
+* Open ``[[ Discuss ]]`` menu
+* RESULT: you can see, that messages not attached to any record now has Reply button
+* Note: messages from Channels (including Direct messages) don’t have this button. You need to open corresponding channel instead.
+
+  * To easily know and navigate to corresponding channel, you need to get module `Show message recipients <https://apps.odoo.com/apps/modules/11.0/mail_to/>`__.
+
+* Note: to see just sent message use one of the following modules:
+
+  * SentBox: https://apps.odoo.com/apps/modules/11.0/mail_sent/
+  * Arhive: https://apps.odoo.com/apps/modules/11.0/mail_archives/
+  * All Messages: https://www.odoo.com/apps/modules/11.0/mail_all/