Add docs foreword

Author: martindurant

docs/source/index.rst

@@ -3,8 +3,24 @@
 
 Welcome to projspec, the projects' project!
 
-The "into" defined this package's scope and sets some definitions. The "quickstart"
-shows some of the concrete things you can actually do.
+There are many ways to organise project-oriented code workflows, and projspec aims
+to give a unified experience, so that you don't have to learn them all. This allows
+for the following types of use-cases:
+
+- *browsing*: a project is _shared_ with you (github, gdrive, your corp's storage solution), and
+  you want to know what it is and what it needs, without downloading and browsing a
+  bunch of readme and scripts.
+- *search*: you have access to a large number of projects on your disk or elsewhere and you want
+  to find the project that meets some criteria like "it uses package X", "it needs
+  dataset Y" or "it can make a conda package". The names of directories alone are not enough.
+- *actions*: you want an app to launch in a single command without diving deeper. This may also
+  extend to "deployment" scenarios where you want to be able to run many kinds of applications
+  without building custom scripts every time.
+- *summaries*: you host projects for your org, and want to know how many are affected by some given
+  CVE, or how many rely on a rust compiler.
+
+The "intro" defined this package's scope and sets some definitions. The "quickstart"
+shows some of the concrete things you can actually do right now.
 
 Introduction to projspec presented at PyData Global 2025: `video`_ | `slides`_