Corrections to README.txt

### Correction 1:
The -u param needs to be capital U: command_line /usr/lib/nagios/plugins/check_drupal -H $HOSTADDRESS$ -U $ARG
What is written:
2. Change the commands.cfg file for Nagios to include the following:

Nagios 2.x:

define command{
command_name check_drupal
command_line /usr/lib/nagios/plugins/check_drupal -H $HOSTADDRESS$ -u $ARG
1$ -T $ARG2$
}

##### Correction 2:
The code for version 2.x and 3.x seems to be swapped by mistake.
Whats written:
4. Defined a service that will run for this host group

Nagios 2.x:

define service{
hostgroup_name drupal-servers
service_description DRUPAL
check_command check_drupal!-U "unique_id" -t 2
use generic-service
notification_interval 0 ; set > 0 if you want to be renotified
}

Nagios 3.x:

define service{
hostgroup_name drupal-servers
service_description DRUPAL
check_command check_drupal!unique_id!2
use generic-service
notification_interval 0 ; set > 0 if you want to be renotified
}