pinwheel/backwards: Adjust reading-material sync through syncthing

Move `books` and into `reading-material`

hosts/pinwheel/modules/syncthing/default.nix

@@ -56,7 +56,7 @@
         };
 
         books = {
-          path = "/home/alex/sync/books";
+          path = "/home/alex/sync/reading-material/books";
           devices = [ "backwards" ];
           versioning = {
             type = "staggered";
@@ -66,8 +66,8 @@
           };
         };
 
-        "reading-material" = {
-          path = "/home/alex/sync/reading-material";
+        ttrpg = {
+          path = "/home/alex/sync/reading-material/ttrpg";
           devices = [ "backwards" ];
           versioning = {
             type = "staggered";