Update DOCKER_INSTALL.md

- full example 
- add postfix integration instructions
- use fastnetmon_notify.py instead of bash

docs/DOCKER_INSTALL.md

@@ -77,3 +77,52 @@ docker build .
 ```
 
 
+To send email, we recommend you to use a external and linked postfix container such:
+
+```
+docker pull panubo/postfix
+
+docker run \
+-e MAILNAME="example.com" \
+-e MYNETWORKS="127.0.0.0/8, 172.16.0.0/12" \
+--name postfix \
+-t panubo/postfix
+```
+
+When you link another container with docker other container name will be added to /etc/hosts pointing to its internal IP. So you can use python script notify (https://github.com/FastVPSEestiOu/fastnetmon/blob/master/src/scripts/fastnetmon_notify.py), instead of bash one.
+
+Just change MAIL_HOSTNAME="localhost" to MAIL_HOSTNAME="postfix" if you start fastnetmon docker container with --link postfix:postfix and create another docker instance with panubo/postfix as --name postfix, for example.
+
+
+A full example of running fastnetmon linked to postfix:
+```
+docker run -a stdin -a stdout -i \
+-v /var/log/fastnetmon_attacks:/var/log/fastnetmon_attacks \
+-v /var/log/fastnetmon.log:/var/log/fastnetmon.log \
+-v /etc/networks_list:/etc/networks_list \
+-v /etc/fastnetmon.conf:/etc/fastnetmon.conf \
+-v /etc/networks_whitelist:/etc/networks_whitelist \
+-v /usr/local/fastnetmon:/usr/local/fastnetmon \
+-v /etc/exabgp_blackhole.conf:/etc/exabgp_blackhole.conf \
+-v /var/log/fastnetmon-notify.log:/var/log/fastnetmon-notify.log \
+-p 10.100.20.2:2055:2055/udp \
+-p 10.100.20.6:2055:2055/udp \
+-p 10.100.20.2:179:179/tcp \
+--name fastnetmon \
+--link postfix:postfix \
+-t robertoberto/fastnetmon:latest /bin/bash
+```
+
+First, you need to create all those files and dirs in main Linux system.
+```
+mkdir /usr/local/fastnetmon
+touch /var/log/fastnetmon_attacks /var/log/fastnetmon.log /etc/networks_list /etc/networks_whitelist /etc/fastnetmon.conf /etc/exabgp_blackhole.conf/var/log/fastnetmon-notify.log
+
+cp /etc/fastnetmon.conf /etc/fastnetmon.conf.bkp
+cp /usr/local/fastnetmon/fastnetmon_notify.py /usr/local/fastnetmon/fastnetmon_notify.py.bkp
+
+wget https://raw.githubusercontent.com/FastVPSEestiOu/fastnetmon/master/src/scripts/fastnetmon_notify.py -O /usr/local/fastnetmon/fastnetmon_notify.py 
+chmod +x /usr/local/fastnetmon/fastnetmon_notify.py 
+wget https://raw.githubusercontent.com/FastVPSEestiOu/fastnetmon/master/src/fastnetmon.conf -O /etc/fastnetmon.conf
+```
+