Add a .gitignore for devtools.

This prevents the working tree from getting dirty each time devtools
is run as a submodule.

BUG=
R=ppi@chromium.org

Review URL: https://codereview.chromium.org/1290743002 .

Cr-Mirrored-From: https://github.com/domokit/mojo
Cr-Mirrored-Commit: cdb117d1d26154dce2beebedfa68487e043a0adc

.gitignore

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..0d20b64
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+*.pyc