Add detail about how images are built and used in README.md

Author: pbchase

Diff for: README.md

@@ -1,3 +1,7 @@
 # RStudio Dockerfile
 
 This project contains a containerized RStudio environment with all REDCap Custodian dependencies bundled in as well as *testthat*, a R testing package. The image is built on push events to this repository, and the resulting image is used in GitHub Actions for STP and Custodian workflows.
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+Built images are pushed to https://github.com/ctsit/rstudio-dockerfile/pkgs/container/rstudio-ci
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+Images can be referenced in the ./.github/workflows/ files in repositoiores that need to use them.