update shelf README

shelf/README.org

@@ -7,20 +7,34 @@ Each Deno scroll:
 
   Unless you're trying to shoot yourself or downstream dep maintainers in the foot.
 - contains a ~scroll.nix~ file
-- defines ~cache-command~ field in ~scroll.nix~
-
-  ~cache-command~ triggers Deno cache build, putting cache in $DENO_DIR.
 - does not use JSR dependencies
 
   They have heavily timestamped metadata and therefore do not support
   reproducible builds.
 - can use NPM dependencies
 
-~.lock~, ~.json~ and ~.jsonc~ files are recursively hashed
-to determine if the cache is updated.
+*** scroll.nix
+- ~name~
+- ~build~
+  + ~cacheCommand~
 
-In that case a new entry needs to be added in knownHashes.
+    The cache command triggers Deno cache build, putting cache in ~$DENO_DIR~.
+  + ~hashFiles~
+  
+    These files are hashed to determine if the cache will be updated.
+
+    In that case a new entry needs to be added in knownHashes.
+  + ~knownHashes~
+
+    An object that maps ~hashFiles~ hashes to this scroll's
+    incremental cache derivation's hash.
+
+    The starting value is just ~{}~, see build logs to determine
+    what needs to be added.
 
 All scrolls currently are to use the same Deno version defined by the flake.
 
-See ~./deno-workflow.nix~ for details.
+Scrolls are automatically discovered by scanning subdirectories of ~./deno~ 
+for those containing a ~scroll.nix~ file.
+
+Directories without ~scroll.nix~ will generate warnings during build.