Add note for 16.04 PHP install

https://community.openenergymonitor.org/t/package-php5-has-no-installation-candidate/575/2

docs/LinuxInstall.md

@@ -8,9 +8,13 @@ You may need to start by updating the system repositories
 
     sudo apt-get update
 
-Install all dependencies:
+on 14.04:
 
     sudo apt-get install apache2 mysql-server mysql-client php5 libapache2-mod-php5 php5-mysql php5-curl php-pear php5-dev php5-mcrypt php5-json git-core redis-server build-essential ufw ntp
+
+on 16.04:
+
+`sudo apt-get install apache2 mysql-server mysql-client php libapache2-mod-php php-mysql php-curl php-pear php-dev php-mcrypt php-json git-core redis-server build-essential ufw ntp`
 
 Install pecl dependencies (serial, redis and swift mailer)