Add testable example in README

This adds a testable example for the README to be able to make the user
experience for new users better.

Makefile

@@ -9,7 +9,7 @@ get-deps:
 	go get -v ./...
 
 .PHONY: test
-test: get-deps metalint check
+test: get-deps metalint docs-check check
 
 .PHONY: check
 check:
@@ -29,7 +29,7 @@ docker-test:
 	docker run -d -p 5432:5432 --name=pgstore_test_1 postgres:9.4
 	sleep 5
 	docker run --rm --link pgstore_test_1:postgres postgres:9.4 psql -c 'create database test;' -U postgres -h postgres
-	PGSTORE_TEST_CONN="postgres://postgres@127.0.0.1:5432/test?sslmode=disable" make check
+	PGSTORE_TEST_CONN="postgres://postgres@127.0.0.1:5432/test?sslmode=disable" make test
 	docker kill pgstore_test_1
 	docker rm pgstore_test_1
 
@@ -37,3 +37,15 @@ docker-test:
 docker-clean:
 	-docker kill pgstore_test_1
 	-docker rm pgstore_test_1
+
+.PHONY: docs-dep
+	which embedmd > /dev/null || go get github.com/campoy/embedmd
+
+.PHONY: docs-check
+docs-check: docs-dep
+	@echo "Checking if docs are generated, if this fails, run 'make docs'."
+	embedmd README.md | diff README.md -
+
+.PHONY: docs
+docs: docs-dep
+	embedmd -w README.md