changed left nav name of prompt guide in index page

Author: Tracey Carter

index.rst

@@ -286,7 +286,7 @@ To keep up to date with changes in the products, see the Splunk Observability Cl
 .. toctree::
    :maxdepth:   3   
 
-   AI Assistant in Observability Cloud <get-started/o11y-ai-promptlibrary>
+   Prompt guide and library for AI Assistant in Observability Cloud <get-started/o11y-ai-promptlibrary>
 
 .. toctree::
    :maxdepth:   3