discuss pip-compile in README

README.md

@@ -4,7 +4,7 @@
 
 A Binder-compatible repo with a `requirements.txt` file.
 
-Access this Binder at the following URL 
+Access this Binder at the following URL
 
 http://mybinder.org/v2/gh/binder-examples/requirements/master
 
@@ -18,7 +18,19 @@ pip install -r requirements.txt
 
 The base Binder image contains no extra dependencies, so be as
 explicit as possible in defining the packages that you need. This includes
-specifying explict versions wherever possible.
+specifying explicit versions wherever possible.
+
+If you do specify strict versions, it is important to do so for *all*
+your dependencies, not just direct dependencies.
+Strictly specifying only some dependencies is a recipe for environments
+breaking over time.
+
+[pip-compile](https://github.com/jazzband/pip-tools/) is a handy
+tool for combining loosely specified dependencies with a fully frozen environment.
+You write a requirements.in with just the dependencies you need
+and pip-compile with generate a requirements.txt with all the strict packages and versions that would come from installing that package right now.
+That way, you only need to specify what you actually know you need,
+but you also get a snapshot of your environment.
 
 In this example we include the library `seaborn` which will be installed in
 the environment, and our notebook uses it to plot a figure.