Update information in README

Author: matthew-brett

README.md

@@ -4,7 +4,33 @@ Installers for the core Scientific Python packages for macOS, Windows, and Linux
 
 <img src="./images/sp_installer_mac.jpg" alt="Screenshot of installer running on macOS" width="450px">
 
-Please visit [the release page](https://github.com/scientific-python/installer/releases/latest) to download an installer for your OS. <!-- TODO: replace with link to tutorial if/when written. -->
+## Who should use these installers?
+
+These installers are double click (macOS, Windows) or simple command line
+installers (Linux) for the standard packages for general scientific Python and
+data science.  The installer includes packages such as:
+
+* Numpy (for arrays)
+* Scipy (extended scientific computing)
+* Matplotlib (plotting)
+* Pandas (data science)
+* Statsmodels (statistics)
+* Scikit-Image (image processing)
+* Scikit-Learn (machine learning and statistics)
+
+as well as many others.  See the `./recipes/scientific-python/construct.yaml`
+file for details.
+
+We imagine these installers will be particularly useful for beginner students
+taking courses in science, statistics or data science, to get them up and
+running with a single download and install step.
+
+## Where can I get the installers?
+
+We will make a release soon.  When we have done so, please visit [the release
+page](https://github.com/scientific-python/installer/releases/latest) to
+download an installer for your OS. <!-- TODO: replace with link to tutorial
+if/when written. -->
 
 ## Development