DOCS UPDATE: Fix incorrect .env file location in Backend Setup instructions

### Is this related to an existing part of the documentation?

- [x] Yes, it is related to an existing section

### What needs to be updated?

## 📌 Current Documentation Issue
The current README instructions for Backend Setup (Section 3) contain incorrect information about where to create the `.env` file and from which directory to run the backend server.

**Specifically:**
- Step 3 instructs users to navigate to the `backend/app` directory (`cd app`)
- Step 4 tells users to create a `.env` file (implying it should be in `backend/app`)
- Step 2 under "Start Development Servers" instructs running the backend from `backend/app` directory

## ✨ Proposed Changes
1. **Remove the misleading navigation step** - Delete step 3 that tells users to `cd app`
2. **Correct the .env file location** - Update the instruction to clearly state: "Create a `.env` file in the backend directory using `.env-example` as a reference"
3. **Update the backend server start command** - Change from `uvicorn main:app --reload` (run from backend/app) to `uvicorn app.main:app --reload` (run from backend directory)
4. **Renumber the steps** accordingly after removing step 3

**Updated Backend Setup section should read:**
- Step 2: Install dependencies
- Step 3: Create `.env` file in the backend directory
- Step 4: Obtain Supabase credentials
- Step 5: Get Groq API key

And the start command should specify running from the `backend` directory with `uvicorn app.main:app --reload`

## 📋 Additional Context
I encountered this issue while setting up the project for GSoC contribution. The setup failed when following the current instructions, and only worked after moving the `.env` file from `backend/app/` to `backend/`.

This is a critical fix as it prevents new contributors from successfully running the project on their first attempt, which can be discouraging for newcomers.

### Relevant Documentation Link (if any)

https://github.com/PulkitDadwal/InPactAI/blob/documentation_fix/README.md

### Record

- [x] I agree to follow this project's Code of Conduct
- [x] I want to work on this update