Update readme.md

I couldn't get the seeding running with the proposed command in readme.

```
python utils/seed_data.py
Connecting to Redis...
Loading data over UDP via Horizon...
Traceback (most recent call last):
  File "utils/seed_data.py", line 25, in <module>
    with open('data.json', 'r') as f:
IOError: [Errno 2] No such file or directory: 'data.json'
```

When starting within the utils directory (where data.json resides) it works.