add .gitignore and hint for testing

Change-Id: Iab067af90a4bd6f76d5f2435aae2f5b483d41439
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..f8b92c3
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+.gradle
+build