Update README.md (Typo Azure Open AI:→Azure OpenAI:)

https://github.com/microsoft/generative-ai-for-beginners/blob/main/15-rag-and-vector-databases/README.md
#PingMSFTDocs

related microsoft#368

15-rag-and-vector-databases/README.md

@@ -30,7 +30,7 @@ After completing this lesson, you will be able to:
 
 For this lesson, we want to add our own notes into the education startup, which allows the chatbot to get more information on the different subjects. Using the notes that we have, learners will be able to study better and understand the different topics, making it easier to revise for their examinations. To create our scenario, we will use:
 
-- `Azure Open AI:` the LLM we will use to create our chatbot
+- `Azure OpenAI:` the LLM we will use to create our chatbot
 
 - `AI for beginners' lesson on Neural Networks`: this will be the data we ground our LLM on