add description for running testcontainers from docker (#110)

* add description for running testcontainers from docker

* adapt suggested changes regarding container wording

Co-authored-by: Till Hoffmann <[email protected]>

* adapt suggested changes regarding build wording

Co-authored-by: Till Hoffmann <[email protected]>

Co-authored-by: Till Hoffmann <[email protected]>

Author: Sebastian Hätälä

README.rst

@@ -51,6 +51,15 @@ The snippet above will spin up a MySql database in a container. The :code:`get_c
 
 More extensive documentation can be found at `Read The Docs <http://testcontainers-python.readthedocs.io/>`_.
 
+Usage within Docker (i.e. in a CI)
+----------------------------------
+
+When trying to launch a testcontainer from within a Docker container two things have to be provided:
+
+1. The container has to provide a docker client installation. Either use an image that has docker pre-installed (e.g. the [official docker images](https://hub.docker.com/_/docker)) or install the client from within the `Dockerfile` specification.
+2. The container has to have access to the docker daemon which can be achieved by mounting `/var/run/docker.sock` or setting the `DOCKER_HOST` environment variable as part of your `docker run` command.
+
+
 Setting up a development environment
 ------------------------------------