Separate reference docs into different block (Azure-Samples#180)

## Purpose
<!-- Describe the intention of the changes being proposed. What problem
does it solve or functionality does it add? -->
* ...
Azure-Samples#175 
## Does this introduce a breaking change?
<!-- Mark one with an "x". -->
```
[ ] Yes
[ ] 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)
[ ] Documentation content changes
[ ] Other... Please describe:
```

## How to Test
*  Get the code

```
git clone [repo-address]
cd [repo-name]
git checkout [branch-name]
npm install
```

* Test the code
<!-- Add steps to run the tests suite and/or manually test -->
```
```

## What to Check
Verify that the following are valid
* ...

## Other Information
<!-- Add any other helpful information that may be needed here. -->

app/backend/Services/ReadRetrieveReadChatService.cs

@@ -112,7 +112,7 @@ standard plan AND dental AND employee benefit.
 
 You answer needs to be a json object with the following format.
 {{
-    ""answer"": // the answer to the question, add a source reference to the end of each sentence. e.g. Apple is a fruit [reference1.pdf]. If no source available, put the answer as I don't know.
+    ""answer"": // the answer to the question, add a source reference to the end of each sentence. e.g. Apple is a fruit [reference1.pdf][reference2.pdf]. If no source available, put the answer as I don't know.
     ""thoughts"": // brief thoughts on how you came up with the answer, e.g. what sources you used, what you thought about, etc.
 }}");