Create documentation to explain how to use server running locally when testing Android app

## Description
As an app developer,
I need to have a backend server up and running,
so that I can test the Android app, for fetching data.

So there can be times when the server is down, but you can still test the Android app, if you run a server locally within the same IP network that your device is using.

We need a document, can be a markdown file (e.g.: gist on GitHub, or a markdown file you put on a docs folder in the repository, ...), describing how you can do this, to help contributors test the app, when the server is down.

## Acceptance Criteria
### Update [Required]
- [ ] Create a document that explains how to test the app using a server hosted on the developer's machine locally.

## Definition of Done
- [ ] All of the required items are completed.
- [x] Approval by 1 mentor.

## Estimation
N/A hours