add line for how to source a script per #832

[harrig12]

Closes #832

Add information to 00-before-we-start.Rmd for how to source a script

[github-actions]

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[tobyhodges]

Thank you for contributing this suggestion, @harrig12. This lesson underwent a major reorganisation when #887 was merged, and the episode that you suggested this Instructor Note be added to no longer exists. Unfortunately, that means I am going to have to close this pull request.

The Working in R and RStudio section of the new content includes instructions for running scripts, and a discussion of the differences between that and running things in the console. If you think the explanation there could be improved, and would be willing to update your fork and open a new pull request suggesting improvements, I or one of the Maintainers will be delighted to review and merge it.