Results: Add .gitattributes file.

Adds .gitattributes file (https://git-scm.com/docs/gitattributes) for
annotaing generated code for GitHub Linguist
(https://github.com/github/linguist).

Author: wlynch

.gitattributes

@@ -0,0 +1,5 @@
+# This file is documented at https://git-scm.com/docs/gitattributes.
+# Linguist-specific attributes are documented at
+# https://github.com/github/linguist.
+
+*.pb.go linguist-generated