I would like to make a recommendation on updating the docs for this page:

https://docs.opennms.com/horizon/30/operation/provisioning/auto-discovery.html

####################################################
Specify the full path to a text file containing one IP address per line to include in discovery. You can embed comments in this file. Any content on a line after a # character is ignored.
 
<include-url>file:filename</include-url>
####################################################

I have found out that you can use the following formats:

<include-url>http://IPADDRESS/filename</include-url>
<include-url>file:///path/to/file/on/local/server</include-url>

There might be more that I have not tested. 

Docs: Add the following to the content:

You can use the following formats:

<include-url>file:filename</include-url>

<include-url>http://IPADDRESS/filename</include-url>
<include-url>file:///path/to/file/on/local/server</include-url>