Update README.md

Author: justbuchanan

README.md

@@ -26,14 +26,14 @@ Diffs are configured with Unified (or ContextDiff) structures, and can
 be output to an io.Writer or returned as a string.
 
 ```Go
-diff := UnifiedDiff{
+diff := difflib.UnifiedDiff{
     A:        difflib.SplitLines("foo\nbar\n"),
     B:        difflib.SplitLines("foo\nbaz\n"),
     FromFile: "Original",
     ToFile:   "Current",
     Context:  3,
 }
-text, _ := GetUnifiedDiffString(diff)
+text, _ := difflib.GetUnifiedDiffString(diff)
 fmt.Printf(text)
 ```