Add instructions and link to instructions

Author: mfisher87

README.md

@@ -39,3 +39,8 @@ are you writing?
 
 * [Learning-oriented tutorial](https://diataxis.fr/tutorials/)
 * [Understanding-oriented explanation](https://diataxis.fr/explanation/)
+
+
+### Workshop environment
+
+Please reference [the instructions in the `docker/` subdirectory](docker/README.md)!

docker/README.md

@@ -22,3 +22,10 @@ It uses familiar
 like conda's `environment.yml` to generate the image, and the author of the repo2docker
 repository doesn't need to deal with frustrating complexities like environment
 activation or requirements to work as expected on a JupyterHub.
+
+
+## Changing dependencies
+
+Edit dependency specifications in `environment.yml`.
+
+You shouldn't need to change any other files.