update README

Author: rscohn2

README.md

@@ -1,2 +1,29 @@
 # container-images
 Dockerfiles for building docker images
+
+There is 1 subdirectory for every image to build. They share a README by symlinking to docker_repo.README.md.
+
+## testing
+
+    python -m pytest tests
+
+Will build every image.
+
+## Adding an image
+
+* copy one of the the existing directories
+* edit the dockerfile
+* add the directory name in test/test_build.py
+* create a new automated build on docker hub, copying build setting of existing image
+
+## Publishing a new release
+
+* Edit the Dockerfiles to refer to the new release
+* Commit changes
+* Tag with the release name
+    git tag -a 2017.0.0 -m 'new release'
+* On dockerhub, edit build settings for all repos to change build rule that generates the image with the latest tag
+* Push changes and tag
+    git push
+    git push origin 2017.0.0
+* Check later that all builds have completed on docker hub