when starting course, replace README

[KatherineCox]

Currently the README is doing double duty - describing OTTR_Template and trying to serve as a reasonable starting point for a README for a course.

I've been working on a C-MOOR branded copy of OTTR_Template, and thought it would be useful to automatically replace the README when starting a course, so that those two concerns can be split up.

This PR

• adds a course_README_template.md to hold the starting point for a course's README
• updates starting-course.yml to replace README.md with course_README_template.md
• moves the course-related content from the existing README.md into course_README_template.md

@cansavvy If you want to make changes to this PR, go for it - I'm handing it off to you. I thought you might have other changes you would want to make to the README content, now that's being split up. I just took the existing content and distributed it between the two files (and updated the link to point to ottrproject.org).

[github-actions[bot]]

No broken urls! :tada: Comment updated at 2023-08-09 with changes from 3e6bf6a61b125db0945ae178b6dc93a67a70b956