Test and Report POST /users/login API

## Description
As a tester,
I need to test /users/login endpoint,
so that we can ensure user is able to login correctly.

You should create a markdown file inside `/docs/manual_tests` with following content:
* Test step by step with dummy data
* Report it as
```
* _Test1 Description_
_Screenshot/gif_:
_Expected Result_:
_Actual Result_:

* _Test2 Description_
_Screenshot/gif_:
_Expected Result_:
_Actual Result_:
```

## Acceptance Criteria
### Update [Required]
- [ ] Tested POST /users/login API
- [ ] Create a markdown file with content mentioned
- [ ] Provide atleast two test cases(1 positive and 1 negative)
### Enhancement to Update [Optional]
- [ ] More test cases can be discussed and can be documented for good
- [ ] Create issue (following Bug Report Template) if expected result is different from actual results

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

## Estimation
2-3 hours