Fix: MCP remove cognee.add() preprequisite from the doc (#1788)

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## Description
This prerequisite is not required because `cognee.add()` is invoked in
the `cognify`. This confuses Claude
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- [ ] New feature (non-breaking change that adds functionality)
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- [ ] Performance improvement
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cognee-mcp/src/server.py

@@ -194,7 +194,6 @@ async def cognify(
 
     Prerequisites:
         - **LLM_API_KEY**: Must be configured (required for entity extraction and graph generation)
-        - **Data Added**: Must have data previously added via `cognee.add()`
         - **Vector Database**: Must be accessible for embeddings storage
         - **Graph Database**: Must be accessible for relationship storage