add hybrid search notebook to "build from scratch" tutorial (#9681)

docs/optimizing/building_rag_from_scratch.md

@@ -85,6 +85,17 @@ maxdepth: 1
 
 These tutorials will show you how to build advanced functionality beyond the basic RAG pipeline. Especially helpful for advanced users with custom workflows / production needs.
 
+### Building Hybrid Search from Scratch
+
+Hybrid search is an advanced retrieval feature supported by many vector databases. It allows you to combine **dense** retrieval with **sparse** retrieval with matching keywords.
+
+```{toctree}
+---
+maxdepth: 1
+---
+Building Hybrid Search from Scratch </examples/vector_stores/qdrant_hybrid.ipynb>
+```
+
 ### Building a Router from Scratch
 
 Beyond the standard RAG pipeline, this takes you one step towards automated decision making with LLMs by showing you how to build a router module from scratch.