Add doc on how to run the tests (#56)

* Fix typo

* Add doc on how to run the tests.

Author: mremond

README.md

@@ -48,7 +48,7 @@ PostgresNIO is a client package for connecting to, authorizing, and querying a P
 
 Support for both simple (text) and parameterized (binary) querying is provided out of the box alongside a `PostgresData` type that handles conversion between PostgreSQL's wire format and native Swift types.
 
-### Motiviation
+### Motivation
 
 Most Swift implementations of Postgres clients are based on the [libpq](https://www.postgresql.org/docs/11/libpq.html) C library which handles transport internally. Building a library directly on top of Postgres' wire protocol using SwiftNIO should yield a more reliable, maintainable, and performant interface for PostgreSQL databases.
 
@@ -210,3 +210,36 @@ print(data.numeric) // PostgresNumeric?
 ```
 
 `PostgresData` is also used for sending data _to_ the server via parameterized values. To create `PostgresData` from a Swift type, use the available intializer methods. 
+
+## Library development
+
+If you want to contribute to the library development, here is how to get started.
+
+### Testing
+
+To run the test, you need to start a local PostgreSQL database using Docker.
+
+If you have Docker installed and running, you can use Docker Compose to start PostgreSQL:
+
+The following command will download the required containers to run the test and start them:
+
+```
+$ docker-compose up -d psql-11
+```
+
+You can choose to run one of the following PostgreSQL version: `psql-11`, `psql-10`, `psql-9`, `psql-ssl`.
+
+From another console or from Xcode, you can then run the test:
+
+```
+$ swift test
+```
+
+You can check that the test are passing, before adding your own to the test suite.
+
+Finally, you can shut down and clean up Docker test environment with:
+
+```
+$ docker-compose down --volumes
+```
+