Create .gitignore and add /.idea there.

Test: git status
Change-Id: Iba3a128b4d071aac42adb6598eab3afe305aec6c
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a09c56d
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/.idea