Add Guidance main section to README.md (#368)

Add Guidance main section to README.md

## Purpose

* Based on @anfibiacreativa feedback, added the Guidance section and
contents to the main Readme file.

## Does this introduce a breaking change?
<!-- Mark one with an "x". -->
```
[ ] Yes
[X] No
```

## Pull Request Type
What kind of change does this Pull Request introduce?

<!-- Please check the one that applies to this PR using "x". -->
```
[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[X] Documentation content changes
[ ] Other... Please describe:
```

## How to Test
*  Get the code

```
git clone [repo-address]
cd [repo-name]
```

## What to Check
Verify that the following are valid
* Review Guidance section in the main Readme file.

README.md

@@ -46,9 +46,10 @@ description: A csharp sample app that chats with your data using OpenAI and AI S
   - [Enabling Application Insights](#enabling-optional-features)
   - [Enabling authentication](#enabling-authentication)
   - [Enable GPT-4V support](#enable-gpt-4v-support)
-- [Productionizing](#productionizing)
-- [Resources](#resources)
-- [FAQ](#faq)
+- [Guidance](#guidance) 
+  - [Productionizing](#productionizing)
+  - [Resources](#resources)
+  - [FAQ](#faq)
 
 # ChatGPT + Enterprise data with Azure OpenAI and Azure AI Search (.NET)
 
@@ -346,7 +347,11 @@ azd down --purge
 azd env set AZD_PREPDOCS_RAN false # This is to ensure that the documents are re-indexed with the new fields.
 ```
 
-## Productionizing
+## Guidance
+
+Besides the tips below, you can find extensive documentation in the [docs](./docs) folder.
+
+### Productionizing
 
 This sample is designed to be a starting point for your own production application,
 but you should do a thorough review of the security and performance before deploying
@@ -366,7 +371,7 @@ to production. Here are some things to consider:
 
 - **Loadtesting**: We recommend running a loadtest for your expected number of users.
 
-## Resources
+### Resources
 
 - [Revolutionize your Enterprise Data with ChatGPT: Next-gen Apps w/ Azure OpenAI and Azure AI Search](https://aka.ms/entgptsearchblog)
 - [Azure AI Search](https://learn.microsoft.com/azure/search/search-what-is-azure-search)