refactor+doc: fix a few issues

* add a README file
* fix broken formatting in packages.bib
* get missing data for sliding-forecasters.qmd online
  instead of local files

Author: dshemetov

README.md

@@ -0,0 +1,22 @@
+# Delphi Tooling Book
+
+The book is a collection of articles and tutorials on how to use the Delphi tooling effectively.
+
+## Compiling the book
+
+The book is written with [Quarto](https://quarto.org/docs/guide/) (which can be installed [here](https://quarto.org/docs/get-started/)). To compile the book, run the following commands:
+
+```sh
+# Install the R dependencies
+R -e 'install.packages(c("pak", "rspm", "renv"))'
+R -e 'renv::restore()'
+
+# Compile the book and preview it
+quarto preview
+```
+
+We use Quarto's freeze feature to re-render only the qmd files that have changed. To force a re-render of a page, run this command:
+
+```sh
+quarto render <name.qmd>
+```

_freeze/archive/execute-results/html.json

@@ -122,7 +122,8 @@ @Manual{R-tidyverse
   author = {Hadley Wickham},
   year = {2023},
   note = {R package version 2.0.0},
-  url = {https://CRAN.R-project.org/package=tidyverse},
+  url = {https://CRAN.R-project.org/package=tidyverse}
+}
 
 @Misc{epidatr2015,
   title = {Delphi Epidata API},