Adds description to context in graph completion and its subclasses (#934)

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## Description
Adds description to context in graph completion and its subclasses

## DCO Affirmation
I affirm that all code in every commit of this pull request conforms to
the terms of the Topoteretes Developer Certificate of Origin.

cognee/modules/retrieval/graph_completion_retriever.py

@@ -50,7 +50,7 @@ class GraphCompletionRetriever(BaseRetriever):
                         content = text
                     else:
                         name = node.attributes.get("name", "Unnamed Node")
-                        content = name
+                        content = node.attributes.get("description", name)
                     nodes[node.id] = {"node": node, "name": name, "content": content}
         return nodes