add CONTRIBUTING file

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644 (file)
index 0000000..ab8b5c6
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1 @@
+Please make sure you format the code using `clang-format -i **/*.[ch]` before sending a pull request.