More 3PID sessions configuration documentation

docs/threepids/email/notifications/smtp-connector.md

@@ -0,0 +1,17 @@
+# Email notifications - SMTP connector
+The following configuration items are available:
+```
+threepid:
+  medium:
+    email:
+      identity:
+        from: 'identityServerEmail@example.org'
+        name: 'My Identity Server'
+      connectors:
+        smtp:
+          host: 'smtpHostname'
+          port: 587
+          tls: 1 # 0 = no STARTLS, 1 = try, 2 = force
+          login: 'smtpLogin'
+          password: 'smtpPassword'
+```