Set East US as the only proposed region to run azd up (#367)

Based on the feedback of issue 344
(#344),
EastUS should be the only proposed region.

## Purpose
Set East US as the default proposed region to deploy all the services.
Based on the feedback

## 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]
```
run `azd up`

Author: elbruno

README.md

@@ -167,7 +167,7 @@ Then, run the following commands to get the project on your local environment:
 Execute the following command, if you don't have any pre-existing Azure services and want to start from a fresh deployment.
 
 1. Run `azd up` - This will provision Azure resources and deploy this sample to those resources, including building the search index based on the files found in the `./data` folder.
-   - For the target location, the regions that currently support the model used in this sample are **East US** or **Sweden Central**. For an up-to-date list of regions and models, check [here](https://learn.microsoft.com/azure/cognitive-services/openai/concepts/models)
+   - For the target location, the regions that currently support the model used in this sample are **East US**. For an up-to-date list of regions and models, check [here](https://learn.microsoft.com/azure/cognitive-services/openai/concepts/models)
    - If you have access to multiple Azure subscriptions, you will be prompted to select the subscription you want to use. If you only have access to one subscription, it will be selected automatically.
 
    > **Note**: