feat(tvix/docs): switch to mdbook

Some of the docs are still outdated (like architecture and drv path
inconsistencies).

Change-Id: I7a6afceb008ef4cd19a764dd6c637b39fa842a2e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11072
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: edef <edef@edef.eu>

web/bubblegum/examples/default.nix

@@ -4,7 +4,6 @@ let
 
   scripts = [
     ./hello.nix
-    ./derivation-svg.nix
     (substituteAll {
       src = ./blog.nix;
       # by making this a plain string this

web/bubblegum/examples/derivation-svg.nix

@@ -1,13 +0,0 @@
-# Warning: this is *very* slow on the first request
-{ depot, ... }:
-
-let
-  inherit (depot.web.bubblegum)
-    respond
-    ;
-in
-respond "OK"
-{
-  Content-type = "image/svg+xml";
-}
-  (builtins.readFile "${depot.tvix.docs.svg}/component-flow.svg")