add readme

README.md

@@ -0,0 +1,23 @@
+# go-type-chains
+`go-type-chains` outputs [Graphviz](https://graphviz.org/) encodings of
+dependencies between files in a Go package.
+
+## Usage
+Say you have a Go package in directory `foo/`. Run
+```
+go-type-chains -p foo/
+```
+to get a Graphviz encoding where each source file in `foo/` is represented by a
+node, and each edge from A to B indicates that A uses a type or value that is
+declared in B.
+
+If you import outside packages, use the `-i` flag to list those packages;
+otherwise the program will error.
+
+## Details
+### Why?
+You *may* find this useful if you have a package with a lot of autogenerated Go
+code that you want to organize into subpackages. (This is the original reason I
+wrote this, although I didn't end up doing any reorganzation on the package I
+was analyzing. But by the time I decided that, I had written enough code that I
+thought I should share.)