Add some background

README.md

@@ -1 +1,24 @@
 # pm: a simple, cross-platform system package manager
+
+`pm` exists amid a set of trade-offs in distributing software. The ideas behind
+`pm` were born at a time when:
+
+- There was no overlap in the Venn diagram of system package managers that
+  offered both strong security promises (signed packages) and permissive
+  licensing (most are GPL).
+- There was reason to suspect that Unix systems might be shipped without
+  scripting languages; software like [brew](https://brew.sh) would cease to
+  work and engineers would be left without a way to fetch and install software.
+- Engineers wanted to deploy software to a variety of Unix-like environments
+  using a single system.
+- Engineers wanted a simple-to-reason-about system that used familiar Unix
+  primitives as building blocks to distribute their software.
+
+Simplicity is a principal design goal of this project. When offered an
+opportunity to chose between two designs the design that requires less mental
+scaffolding to describe or implement should be used. As a concrete example:
+transitive dependency calculations are implemented, but supporting compatible
+version *ranges* are not.
+
+The project is currently in early design phases, and this document describes
+the high-level approach of the project.