fix: Add Docker setup for the L402 payment gateway

[Xanoutas]

Fix for #3: Add Docker setup for the L402 payment gateway

# lightning_memory/Dockerfile
FROM python:3.9-slim

WORKDIR /app

COPY requirements.txt requirements.txt
RUN pip install --no-cache-dir -r requirements.txt

COPY . .

CMD ["python", "lightning_memory/server.py"]

# docker-compose.yml
version: '3.8'

services:
  l402-gateway:
    build: .
    ports:
      - "8000:8000"
    depends_on:
      - phoenixd

  phoenixd:
    image: phoenixd:latest
    ports:
      - "5000:5000"

# lightning_memory/README.md
# Lightning Memory

This repository contains the implementation of the Lightning Memory system, including the L402 payment gateway.

## Docker Setup

To run the L402 payment gateway with Docker, follow these steps:

1. **Build the Docker image:**
   ```sh
   docker-compose build

2. Start the services:

   docker-compose up

This will start both the L402 gateway and the Phoenixd sidecar. The L402 gateway will be accessible on port 8000, and Phoenixd will be accessible on port 5000.

### Explanation of Changes

1. **Dockerfile**:
   - Created a Dockerfile to build the image for the L402 payment gateway.
   - The image uses Python 3.9-slim as the base image.
   - Installs dependencies from `requirements.txt`.
   - Copies the application code into the container.
   - Sets the command to run the server.

2. **docker-compose.yml**:
   - Added a `docker-compose.yml` file to define the services for the L402 gateway and Phoenixd.
   - The `l402-gateway` service builds from the Dockerfile and maps port 8000.
   - The `phoenixd` service uses a pre-built image and maps port 5000.
   - The `l402-gateway` service depends on `phoenixd` to ensure it starts after Phoenixd.

3. **README.md**:
   - Updated the README to include instructions for setting up and running the application using Docker.

These changes provide a straightforward way to deploy the L402 payment gateway and its dependencies using Docker and docker-compose.

---
Closes #3

> Auto-generated fix | deepseek-coder:33b (RTX 5070)
> EVM: `0x22FD4d24771358fD18a3964456CD5F9d7b6E8f9f` | SOL: `C4PcQjqDW4a5Pvhx5ZFPvAodkGiVG49q8dMvpskqSvuH`