update @mention CTA for Enterprise users

Author: kalanchan

docs/cody/prompts-guide.mdx

@@ -95,6 +95,12 @@ Cody leverages the `@-mention` syntax to source context via files, symbols, web
 
 You can learn more about context [here](/cody/core-concepts/context).
 
+### Indexing your repositories for context
+@-mention local and current repositories are only available if you have your repository indexed. Enterprise and Enterprise Starter users can request their admins to add their local project for indexing to get access to @-mention context. 
+
+Repository indexing is only available to [Tier 1 Code Hosts](https://sourcegraph.com/docs/admin/code_hosts), please reach out to your admins if you require assistance with indexing. 
+
+
 ## Selecting the right LLM
 
 Cody offers a variety of LLMs for both chat and in-line edits by all the leading LLM providers. Each LLM has its strengths and weaknesses, so it is important to select the right one for your use case. For example, Claude 3.5 Sonnet and GPT-4o are powerful for code generation and provide accurate results. However, Gemini 2.0 Flash is a decent choice for cost-effective searches. So, you can always optimize your choice of LLM based on your use case.