Update llama_index imports (#849)

Going through the tutorial I found that llama_index was restructured
recently (in the last month?) so these imports had to be changed to work
correctly

Author: sestinj

docs/howtos/applications/compare_embeddings.md

@@ -81,8 +81,8 @@ refer to [langchain-tutorial](../integrations/langchain.ipynb) see how to evalua
 ```{code-block} python
 
 import nest_asyncio
-from llama_index import VectorStoreIndex, SimpleDirectoryReader, ServiceContext,OpenAIEmbedding
-from langchain.embeddings import HuggingFaceEmbeddings
+from llama_index.core import VectorStoreIndex, SimpleDirectoryReader, ServiceContext
+from langchain.embeddings import HuggingFaceEmbeddings, OpenAIEmbeddings
 import pandas as pd
 
 nest_asyncio.apply()
@@ -158,4 +158,4 @@ result_df.head()
 
 <p align="left">
 <img src="../../_static/imgs/compare-emb-results.png" alt="results" width="800" height="600" />
-</p>
+</p>