Fix links that are carried over from Getting Started

[avahoffman]

AnVIL_Book_Instructor_Guide/04_Developing_content.Rmd

Line 16 in b060b8b

1. You need to set up [Billing](#account-setup-instructors). This includes your Google Billing Account and Terra Billing Project. Take note of your Terra Billing Project name.

AnVIL_Book_Instructor_Guide/04_Developing_content.Rmd

Line 20 in b060b8b

1. Launch RStudio using the Community-Maintained RStudio Environment. This requires you to be familiar with [RStudio on AnVIL](#starting-rstudio).

These no longer link to anything. Replace links.