Add .gitignore so 'repo status' doesn't show errors.pyc.

...also ignore emacs backup files (ending with ~) while we're at it.

BUG=none
TEST=Ran 'pre-upload.py', saw errors.pyc, ran 'repo status'.

Change-Id: I77894c89bf0cf5f2dffda1a8c531ca3c38280f7d
Reviewed-on: http://gerrit.chromium.org/gerrit/1030
Reviewed-by: Ryan Cui <rcui@chromium.org>
Tested-by: Doug Anderson <dianders@chromium.org>
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..20665e7
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+# Generated files
+*.pyc
+*~