Template Documentation should mention that template files must end in '-templates.xml'

[Mark Pointing]

Firstly AWESOME WORK on glabels-qt! This is one of those open source projects that is better than commercial alternatives. Thank you for your efforts!

Whilst trying to create a template, I was perplexed for several hours as to why my template was not being picked up by glabels-qt. It was because I named it brother-tapes.xml renaming it to brother-tapes-templates.xml caused it to be loaded.

A simple change to glabels-qt/docs/PRODUCT-TEMPLATES.md would have eliminated this confusion. Simply change the third line of text to something like this:

gLabels searches for templates in files with names ending in -templates.xml at several locations as described here:

I can file a PR if needed.