Update README

README.md

@@ -1,18 +1,18 @@
-High-level architecture:
+## High-level architecture
 
 ```mermaid
 flowchart TD
     Cellar[Cellar API]
-    Frontend
+    Frontend[React Frontend]
 
-    subgraph backend
+    subgraph "FastAPI backend"
         client[Cellar Client]
-        conv[Formex -> HTML converter]
-        FastAPI
+        conv[Formex -> HTML renderer]
+        FastAPI[REST API]
     end
 
     Cellar --> meta@{ shape: docs, label: "XML/RDF Metadata"}
-    Cellar --> docs@{ shape: docs, label: "Formex/XHTML/PDF text"}
+    Cellar --> docs@{ shape: docs, label: "Formex 4 content"}
 
     meta --> client
     docs --> client
@@ -24,3 +24,13 @@ flowchart TD
 
     FastAPI -- TOC, HTML article text --> Frontend
 ```
+
+## Resources
+
+- Formex 4
+  - [XML schema](https://op.europa.eu/documents/3938058/5910419/formex_manual_on_screen_version.html/)
+  - [Physical specifications](https://op.europa.eu/documents/3938058/5896514/physical-specifications/)
+- [Cellar](https://op.europa.eu/en/web/cellar/home)
+  - [Publications API](https://op.europa.eu/en/web/cellar/cellar-data/publications)
+  - [Metadata REST API](https://op.europa.eu/en/web/cellar/cellar-data/metadata/metadata-notices)
+  - [Metadata SPARQL API](https://op.europa.eu/en/web/cellar/cellar-data/metadata/knowledge-graph)