Update COVID-19 webpage

- Prefer hosting on sandbox.wpcarro.dev; I would prefer to host it at
  sandbox.wpcarro.dev/covid-19, but I haven't figure out how to use Nginx to do
  serve locations like /covid-19 yet.
- Splice the src directory: When I develop locally and index.html exists within
  ./src, I cannot access ./node_modules because ./node_modules is in a parent
  directory. I could fix this if I used a bundler like Parcel or Webpack, but I
  do not want to set that up at this time.
- Introduce Tailwind for CSS. This complicates my build a bit as well. For now,
  I'm including output.css even though ideally I should not version-control this
  file. I haven't figured out how to `yarn install` and run commands like `npx
  tailwindcss build styles.css -o output.css` in a Nix derivation yet. Hopefully
  I will learn and refactor this.
- Add some content about why I made this chart
- Add some content about some of my covid-19 predictions
- Add a footer to the webpage
- Delete timeseries.json and prefer fetching the published data instead

nixos/socrates/configuration.nix

@@ -164,7 +164,7 @@ in {
         enableACME = true;
         root = briefcase.blog;
       };
-      "wpcarro.dev" = {
+      "sandbox.wpcarro.dev" = {
         addSSL = true;
         enableACME = true;
         root = briefcase.covid-uk;
@@ -172,5 +172,5 @@ in {
     };
   };
 
-  system.stateVersion = "20.09"; # Did you read the comment?
+  system.stateVersion = "20.09";
 }