user_template is not well defined

[Roberto Batty]

Describe the bug
There's not much to say, I wanted to redefine responses.def template, and I followed the instructions that indicate I must copy parent and child, so I copied main.dot and responses.def, and it wasn't enough, didn't work

and I managed to find that operation.dot was also required to modify responses.def.

but operation.dot references a many files inside, so:

this is my custom templates folder

this should be in the documentation, or at least show few more cases/examples of using --user_templates

thank you.

To Reproduce
Steps to reproduce the behavior:

1. Command-line:

widdershins --language_tabs 'javascript:JavaScript' 'http:HTTP' --user_templates './documentation/templates' --summary documentation/openapi3.json -o documentation/slate/index.md

Versions:

• 18.15.0

[Mike Ralphson]

We call this out in the README:

This means that it is usually easiest to copy all .dot and .def files to your user templates directory so you don't skip a template or partial.