Clarify that contributors agree with MIT license in `CONTRIBUTING.md`.
# How to contribute
mruby is an open-source project which is looking forward to each contribution.
+Contributors agree to license their contribution(s) under MIT license.
## Your Pull Request
@@ -47,11 +48,13 @@ on-demand.
#### Insert a break after the function return value:
+ ```C
int
main(void)
{
...
}
+ ```
### Ruby code
