Adding tutorial on how to customize the workshop template with the links to corresponding lessons

[leilaicruz]

I was trying to set up my own template for a software carpentry to practice how to set a self organized workshop using your template. And it is very clear how you can customize your personal information and which setup to use based on the the type of carpentry, yet the lessons are not documented how to include them. Or at least , it is not clear at all from someone novice on how to tweak files on setting website templates , how to include the proper program of the lesson with the proper links to the material.
I figured it out a way by looking at (https://softwaresaved.github.io/2020-10-13-ssi-online/). In summary is including the syllabus.html inside the _include folder and in the index.md , then putting corresponding links in the schedule.html per carpentry lesson.You can see it in my copy of the template repo (https://github.com/leilaicruz/example-workshop-online)

This would be useful to get all the setup and the required material all in one place.
Just let me know if a pull request would be needed to integrate these changes in the template.

thanks!