git-ignore files generated by "./tools/build_docs.sh ."

Change-Id: Ibf190998e52e7814ddc7f7ab4cf174aee28df9bf
diff --git a/.gitignore b/.gitignore
index 798b081..0c22c6b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -13,3 +13,5 @@
 accrc
 .stackenv
 .prereqs
+docs/
+docs-files