samples: Add .gitignore to ignore output files

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/samples/zephyr/.gitignore b/samples/zephyr/.gitignore
new file mode 100644
index 0000000..a8a0dce
--- /dev/null
+++ b/samples/zephyr/.gitignore
@@ -0,0 +1 @@
+*.bin