Linux.md in pghero-2.1.1

- old
+ new

@@ -2,10 +2,11 @@
 
 Distributions
 
 - [Ubuntu 16.04 (Xenial)](#ubuntu-1604-xenial)
 - [Ubuntu 14.04 (Trusty)](#ubuntu-1404-trusty)
+- [Debian 9 (Stretch)](#debian-9-stretch)
 - [Debian 8 (Jesse)](#debian-8-jesse)
 - [Debian 7 (Wheezy)](#debian-7-wheezy)
 - [CentOS / RHEL 7](#centos--rhel-7)
 - [SUSE Linux Enterprise Server 12](#suse-linux-enterprise-server-12)
 
@@ -31,10 +32,21 @@
   https://dl.packager.io/srv/pghero/pghero/master/installer/ubuntu/14.04.repo
 sudo apt-get update
 sudo apt-get -y install pghero
 ```
 
+### Debian 9 (Stretch)
+
+```sh
+sudo apt-get -y install apt-transport-https
+wget -qO- https://dl.packager.io/srv/pghero/pghero/key | sudo apt-key add -
+sudo wget -O /etc/apt/sources.list.d/pghero.list \
+  https://dl.packager.io/srv/pghero/pghero/master/installer/debian/9.repo
+sudo apt-get update
+sudo apt-get -y install pghero
+```
+
 ### Debian 8 (Jesse)
 
 ```sh
 sudo apt-get -y install apt-transport-https
 wget -qO- https://dl.packager.io/srv/pghero/pghero/key | sudo apt-key add -
@@ -245,9 +257,15 @@
 Minimum connections for high connections warning
 
 ```sh
 sudo pghero config:set PGHERO_TOTAL_CONNECTIONS_THRESHOLD=100 # default
 ```
+
+Statement timeout for explain
+
+```sh
+sudo pghero config:set PGHERO_EXPLAIN_TIMEOUT_SEC=10 # default
+````
 
 ## Upgrading
 
 Ubuntu and Debian
 