remove old link and remove "unstable" now that it's used in prod

Author: sqs

README.md

@@ -2,8 +2,6 @@
 
 Diff parser and printer for Go.
 
-**Unstable API:** go-diff is currently in development. If you depend on it, you should vendor it.
-
 Installing
 ----------
 
@@ -14,7 +12,7 @@ go get -u sourcegraph.com/sourcegraph/go-diff/diff
 Usage
 -----
 
-It doesn't actually compute a diff. It only reads in (and prints out, given a Go struct representation) unified diff output, such as the following. The corresponding data structure in Go is the [`diff.FileDiff`](https://sourcegraph.com/github.com/sourcegraph/go-diff/-/def/GoPackage/github.com/sourcegraph/go-diff/diff/-/FileDiff) struct.
+It doesn't actually compute a diff. It only reads in (and prints out, given a Go struct representation) unified diff output, such as the following. The corresponding data structure in Go is the `diff.FileDiff` struct.
 
 ```diff
 --- oldname	2009-10-11 15:12:20.000000000 -0700