Add instructions to start up libpostal + placeholder before starting pelias

[jpan127]

Start the API

After installing placeholder, start the service by navigating to the directory you installed it in, and running:

PORT=3000 npm start;

The port number 3000 corresponds to the port you specified in api.services.placeholder.url.

After installing go-whosonfirst-libpostal, start the service by navigating to the directory you installed it in, and running:

./bin/wof-libpostal-server -port 8080

The port number 8080 corresponds to the port you specified in api.services.libpostal.url (defaults to 8080).

Now that the API knows how to connect to Elasticsearch and all other Pelias services, all that is
required to start the API is:

npm start

[kylebarron]

@orangejulius I was also having trouble figuring out how to start the libpostal server. Is go-whosonfirst-libpostal the intended way to start a libpostal server?