Enhance documentation and automate R package management

Update documentation to reflect that all tools are provided via a builder Docker image

- Simplify prerequisites section in Readme.md
- Add detailed explanation of the builder image and its role
- Document R package caching mechanism for faster builds
- Update start-jupyterhub.sh to build and use the builder image
- Add Dockerfile.builder to provide the build environment
- Implement automatic R dependency detection and installation
- Update Slides.qmd to use gt package for better table formatting

.gitignore

@@ -5,6 +5,7 @@
 /jupyterhub_volumes/caddy
 /jupyterhub_volumes/course/data/Genbank
 /jupyterhub_volumes/web/
+/jupyterhub_volumes/builder
 /**/.DS_Store
 /web_src/**/*.RData
 /web_src/**/*.pdf
@@ -16,4 +17,4 @@
 ncbitaxo_*
 Readme_files
 Readme.html
-tmp.*
+tmp.*