Edit example env file to use postgrs container IP

[UTXOnly]

Edited the example .env file in README to use postgres container ip instead of localhost

This issue was raised in #45

This should hopefully resolve the error below:

event_handler_1      |  Is the server running on that host and accepting TCP/IP connections?
event_handler_1      | INFO:     172.28.0.2:52276 - "POST /new_event HTTP/1.1" 500 Internal Server Error
event_handler_1      | ERROR:    Exception in ASGI application
event_handler_1      | Traceback (most recent call last):
event_handler_1      |   File "/app/event_handler.py", line 114, in handle_new_event
event_handler_1      |     async with request.app.async_pool.connection() as conn:
event_handler_1      |   File "/usr/local/lib/python3.9/contextlib.py", line 181, in __aenter__
event_handler_1      |     return await self.gen.__anext__()
event_handler_1      |   File "/usr/local/lib/python3.9/site-packages/psycopg_pool/pool_async.py", line 190, in connection
event_handler_1      |     conn = await self.getconn(timeout=timeout)
event_handler_1      |   File "/usr/local/lib/python3.9/site-packages/psycopg_pool/pool_async.py", line 225, in getconn
event_handler_1      |     raise PoolTimeout(
event_handler_1      | psycopg_pool.PoolTimeout: couldn't get a connection after 30.00 sec