message: Document PORT env variable, fix coveralls link
diff: -# Postcodes.io [![Build Status](https://travis-ci.org/ideal-postcodes/postcodes.io.png)](https://travis-ci.org/ideal-postcodes/postcodes.io) [![Coverage Status](https://coveralls.io/repos/github/goingdotin/postcodes.io/badge.svg?branch=master)](https://coveralls.io/github/goingdotin/postcodes.io?branch=master)
  +# Postcodes.io [![Build Status](https://travis-ci.org/ideal-postcodes/postcodes.io.png)](https://travis-ci.org/ideal-postcodes/postcodes.io) [![Coverage Status](https://coveralls.io/repos/github/ideal-postcodes/postcodes.io/badge.svg?branch=master)](https://coveralls.io/github/ideal-postcodes/postcodes.io?branch=master)
  Query for UK postcodes and geolocations over HTTP. Postcodes.io uses the Office for National Statistics Postcode Directory.
  @@ -60,6 +60,7 @@ Configuration available via Environment Variables:
  - `POSTGRES_DATABASE`
  - `POSTGRES_HOST`
  - `POSTGRES_PORT`
  +- `PORT`
  ## Testing
  