Add more instructions for running tests (#750)

What
===
Add more instructions for running tests.

Why
===
For those starting out and not familiar with how to get a PostgresSQL
up and running for tests some examples would be helpful.

README.md

@@ -14,18 +14,7 @@ documentation at <http://godoc.org/github.com/lib/pq>.
 
 ## Tests
 
-`go test` is used for testing.  A running PostgreSQL server is
-required, with the ability to log in.  The default database to connect
-to test with is "pqgotest," but it can be overridden using environment
-variables.
-
-Example:
-
-	PGHOST=/run/postgresql go test github.com/lib/pq
-
-Optionally, a benchmark suite can be run as part of the tests:
-
-	PGHOST=/run/postgresql go test -bench .
+`go test` is used for testing.  See [TESTS.md](TESTS.md) for more details.
 
 ## Features
 

TESTS.md

@@ -0,0 +1,33 @@
+# Tests
+
+## Running Tests
+
+`go test` is used for testing. A running PostgreSQL
+server is required, with the ability to log in. The
+database to connect to test with is "pqgotest," on
+"localhost" but these can be overridden using [environment
+variables](https://www.postgresql.org/docs/9.3/static/libpq-envars.html).
+
+Example:
+
+	PGHOST=/run/postgresql go test
+
+## Benchmarks
+
+A benchmark suite can be run as part of the tests:
+
+	go test -bench .
+
+## Example setup (Docker)
+
+Run a postgres container:
+
+```
+docker run --expose 5432:5432 postgres
+```
+
+Run tests:
+
+```
+PGHOST=localhost PGPORT=5432 PGUSER=postgres PGSSLMODE=disable PGDATABASE=postgres go test
+```