Update Aeon diagram (#3593)

Provide text alternative to graphic
Mention the possibility that the Reading Room Request button can link directly to aeon
Mention the case of a multi-item resource

docs/requests/aeon.md

@@ -1,15 +1,52 @@
+### Aeon requests integration
+
+#### Sequence of a request
+
+An Aeon request goes through the following steps, as illustrated by the diagram below:
+
+1. Patron goes to record show page
+1. Catalog fetches holdings locations list from bibdata (if not cached)
+1. If the item location is an aeon_location:
+    1. If the resource is relatively simple:
+        1. Catalog generates an OpenURL
+        1. Catalog renders Reading Room Request button that links directly to aeon
+        1. Patron presses button to go to aeon.
+    1. If the resource is more complex:
+        1. Catalog renders Reading Room Request button that links to requests controller
+        1. Patron presses Reading Room Request button
+        1. If it's a single item:
+            1. Catalog generates an OpenURL
+            1. Catalog redirects to generated OpenURL
+        1. If it's multiple items:
+            1. Catalog generates an OpenURL for each item
+            1. Catalog renders a Reading Room Request button that links directly to aeon for each item
+            1. Patron presses button to go to aeon
+
 ```mermaid
 sequenceDiagram
-%%{init: {'theme': 'neutral'}}%%
     title Placing an aeon request
     actor patron as Patron
     patron->>Catalog: Go to record show page
     Catalog->>Bibdata: Request holdings locations list (if not cached)
     Bibdata->>Catalog: Holding locations list
     opt item location is an aeon_location
-      Catalog->>patron: Show Reading Room Request button
-      patron->>Catalog: Press Reading Room Request button
-      Catalog->>Catalog: Generate an OpenURL
-      Catalog->>Aeon: Redirect to generated OpenURL
+      opt resource is relatively simple
+        Catalog->>Catalog: Generate an OpenURL
+        Catalog->>patron: Render Reading Room Request button<br>that links directly to aeon
+        patron->>Aeon: Press button to go to aeon
+      end
+      opt resource is more complex
+        Catalog->>patron: Render Reading Room Request button<br>that links to requests controller
+        patron->>Catalog: Press Reading Room Request button
+        opt single item
+          Catalog->>Catalog: Generate an OpenURL
+          Catalog->>Aeon: Redirect to generated OpenURL
+        end
+        opt multiple items
+          Catalog->>Catalog: Generate OpenURLs for each item
+          Catalog->>patron: Render Reading Room Request button that links<br>directly to aeon for each item
+          patron->>Aeon: Press button to go to aeon
+        end
+      end
     end
 ```