Adding CONTRIBUTING.md to point to nilrt CONTRIBUTING.md
Adding CONTRIBUTING.md to point to nilrt CONTRIBUTING.md

Signed-off-by: Charlie Johnston <b1dee96d22a970fd24786261fc8c6eb1012b2c10@ni.com>

ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt