chore : Add README and setup instructions for dice_agent_rest sample

samples/python/agents/dice_agent_rest/README.md

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+# ADK A2A Dice Roll REST Agent Example
+
+This example shows how to build a small **tool-using LLM agent** with the **Google Agent Development Kit (ADK)**, designed to be exposed over REST (and/or A2A).  
+The agent:
+
+- Rolls an N-sided dice on request.
+- Checks whether numbers are prime using a tool.
+- Keeps **conversational state** via in-memory sessions.
+- Supports **streaming responses**, suitable for REST, WebSockets, or A2A.
+
+## 1. Prerequisites
+
+- **Python** 3.11 or higher  
+  ```bash
+  python3 --version  # On macOS/Linux; use `python --version` on Windows
+  ```
+- **Git** (if you need to clone the repo)  
+  ```bash
+  git --version
+  ```
+
+## 2. Get the Source Code
+
+If you don’t have the repo yet:
+
+```bash
+git clone https://github.com/google/a2a-samples.git
+cd a2a-samples/samples/python/agents/dice_agent_rest
+```
+
+If you already have it:
+
+```bash
+cd a2a-samples/samples/python/agents/dice_agent_rest
+```
+
+
+## 3. Create and Activate a Virtual Environment
+
+### macOS / Linux
+
+```bash
+python3 -m venv .venv
+source .venv/bin/activate
+```
+
+### Windows (PowerShell)
+
+```powershell
+python -m venv .venv
+.\.venv\Scripts\activate
+```
+
+You should now see `(.venv)` in your terminal prompt.
+
+
+## 4. Install Dependencies
+
+You can use **`uv`** (if installed) or **`pip`**.
+
+### Option A: Using `uv` (uses `uv.lock`)
+
+From the `dice_agent_rest` directory:
+
+```bash
+uv sync
+```
+
+(Optional sanity check for uv environment):
+
+```bash
+uv run python -c "print('uv environment ready')"
+```
+
+### Option B: Using `pip`
+
+Make sure your virtual environment is active (`(.venv)` visible), then run:
+
+```bash
+pip install .
+```
+
+(Optional, if you want editable mode while developing):
+
+```bash
+pip install -e .
+```
+
+
+## 5. Set the Google GenAI API Key
+
+You must set `GOOGLE_API_KEY` before running anything that calls Gemini.
+
+### macOS / Linux
+
+```bash
+export GOOGLE_API_KEY="YOUR_API_KEY_HERE"
+```
+
+### Windows (PowerShell)
+
+```powershell
+$Env:GOOGLE_API_KEY = "YOUR_API_KEY_HERE"
+```
+
+Verify:
+
+```bash
+echo $GOOGLE_API_KEY      # macOS / Linux
+```
+
+```powershell
+echo $Env:GOOGLE_API_KEY  # Windows PowerShell
+```
+
+
+## 6. Environment Sanity Check
+
+With the virtual environment active and dependencies installed:
+
+```bash
+python -c "import google.adk, google.genai; print('Environment OK')"
+```
+
+If you see `Environment OK` with no errors, the setup is complete.