Ignore /.idea and *.iml files

Historically the .idea directory was created in the root of the
checkout. Now we generate the .idea directory in frameworks/base, so we
need to start ignoring it here.

Test: git status
Change-Id: I9b8142768173f3db153fda494f0c49697b703a38
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..45884c4
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/.idea
+*.iml