add instructions for docker regtest mode

docs/interactive_regtest_macos.md

@@ -1,3 +1,33 @@
+# Using docker
+
+You can setup our integration test with docker.
+
+First, pull the integration test container from quay.
+
+```
+docker pull quay.io/blockstack/blockstack-core-with-regtest:develop
+```
+
+Then, start the docker container:
+
+```
+docker run -dt -p 6270:6270 -v /tmp:/tmp -e BLOCKSTACK_TEST_CLIENT_RPC_PORT=6270 -e BLOCKSTACK_TEST_CLIENT_BIND=0.0.0.0 quay.io/blockstack/blockstack-core-with-regtest:develop blockstack-test-scenario --interactive 2 blockstack_integration_tests.scenarios.portal_test_env
+```
+
+You can see the running container:
+
+```
+$ docker ps
+```
+
+And the setup has completed:
+
+```
+$ IMAGE=$(docker ps | grep "quay.io/blockstack/blockstack-core-with-regtest:develop" | awk '{ print $1 }')
+$ docker logs -f $IMAGE | grep inished
+
+```
+
 
 # Install bitcoind