Update status and add example in README

Author: bluekeyes

README.md

@@ -1,14 +1,33 @@
 # go-gitdiff
 
+[![GoDoc](https://godoc.org/github.com/bluekeyes/go-gitdiff/gitdiff?status.svg)](http://godoc.org/github.com/bluekeyes/go-gitdiff/gitdiff)
+
 A Go library for parsing and applying patches generated by `git diff`, `git
 show`, and `git format-patch`. It can also parse and apply unified diffs
 generated by the standard `diff` tool.
 
-It supports both standard line-oriented / text patches and Git binary patches.
+It supports both standard line-oriented text patches and Git binary patches.
+
+```golang
+patch, err := os.Open("changes.patch")
+if err != nil {
+    log.Fatalf(err)
+}
+
+files, preamble, err := gitdiff.Parse(patch)
+if err != nil {
+    log.Fatalf(err)
+}
+
+// files is a slice of *gitdiff.File describing the files changed in the patch
+// preamble is a string of the content of the patch before the first file
+```
 
 ## Status
 
-In development, most functionality is currently missing, incomplete, or broken.
+In development, expect API changes. Patch parsing works, but has not been
+tested extensively against real-world patches. Patch application has not been
+implemented yet.
 
 ## Why another git/unified diff parser?