gitignore: ignore intellij files

BUG=None
TEST=None

Change-Id: I560a1fedb18b95141fd3cd6c794a2eca0e3fe1ba
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/tnull/+/2577195
Tested-by: Sean Abraham <seanabraham@chromium.org>
Auto-Submit: Sean Abraham <seanabraham@chromium.org>
Reviewed-by: Brigit Rossbach <brigitr@google.com>
Commit-Queue: Brigit Rossbach <brigitr@google.com>
diff --git a/.gitignore b/.gitignore
index ea110e0..b8aaa68 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,6 @@
 .cipd_bin/*
 *.pb.go
 descpb.bin
+
+# IDEs and editors
+/.idea