fix documentation, closes #1816

Author: oesteban

doc/devel/testing_nipype.rst

@@ -107,26 +107,47 @@ This will skip any tests that require matlab.
 Testing Nipype using Docker
 ---------------------------
 
-As of :code:`nipype-0.13`, Nipype is tested inside Docker containers. Once the developer
-`has installed the Docker Engine <https://docs.docker.com/engine/installation/>`_, testing
-Nipype is as easy as follows::
+As of :code:`nipype-0.13`, Nipype is tested inside Docker containers. First, install the
+`Docker Engine <https://docs.docker.com/engine/installation/>`_.
+Nipype has one base docker image called nipype/nipype, and several additional test images
+for various Python versions.
+
+The base nipype/nipype image is built as follows::
 
   cd path/to/nipype/
-  docker build -f docker/nipype_test/Dockerfile_py27 -t nipype/nipype_test:py27
-  docker run -it --rm -v /etc/localtime:/etc/localtime:ro \
-                      -e FSL_COURSE_DATA="/root/examples/nipype-fsl_course_data" \
+  docker build -t nipype/nipype .
+
+This base image contains several useful tools (FreeSurfer, AFNI, FSL, ANTs, etc.) and
+a nipype installation, all in Python 3.5.
+It is possible to fetch a built image from the latest master branch of nipype
+using::
+
+  docker run -it --rm nipype/nipype:master
+
+
+The docker run command will then open the container and offer a bash shell for the
+developer.
+
+The additional test images have several test scripts installed. For instance,
+to build and run all tests on Python 2.7::
+
+  cd path/to/nipype/
+  docker build -f docker/Dockerfile_py27 -t nipype/nipype_test:py27 .
+  docker run -it --rm -e FSL_COURSE_DATA="/root/examples/nipype-fsl_course_data" \
                       -v ~/examples:/root/examples:ro \
                       -v ~/scratch:/scratch \
                       -w /root/src/nipype \
-                      nipype/nipype_test:py27 /usr/bin/run_pytest.sh
+                      nipype/nipype_test:py27 /usr/bin/run_pytests.sh
 
 For running nipype in Python 3.5::
 
   cd path/to/nipype/
-  docker build -f docker/nipype_test/Dockerfile_py35 -t nipype/nipype_test:py35
-  docker run -it --rm -v /etc/localtime:/etc/localtime:ro \
-                      -e FSL_COURSE_DATA="/root/examples/nipype-fsl_course_data" \
+  docker build -f docker/Dockerfile_py35 -t nipype/nipype_test:py35 .
+  docker run -it --rm -e FSL_COURSE_DATA="/root/examples/nipype-fsl_course_data" \
                       -v ~/examples:/root/examples:ro \
                       -v ~/scratch:/scratch \
                       -w /root/src/nipype \
-                      nipype/nipype_test:py35 /usr/bin/run_pytest.sh
+                      nipype/nipype_test:py35 /usr/bin/run_pytests.sh
+
+The last two examples assume that the example data is downladed into ~/examples and
+the ~/scratch folder will be created if it does not exist previously.