Add note about running autoreconf to get configure file

Author: RincewindsHat

README.md

@@ -18,12 +18,21 @@ apt-get update
 apt-get -y install git build-essential libsnmp-dev
 ```
 
+
 Download and extract the tarball from https://github.com/NETWAYS/check_interfaces/releases
 
 ```
 ./configure --libexecdir=/usr/lib/nagios/plugins
 ```
 
+or clone this repository and regenerate the autoconf scripts
+
+```
+autoreconf
+./configure --libexecdir=/usr/lib/nagios/plugins
+```
+
+
 Running "make" should successfully compile the plugin, and "make install" will install them under
 the configured path.