changes the relative URL in the PR template to an absolute URL
to resolve a "Not Found" error.
Signed-off-by: Wesley Gimenes <redacted>
## ✅ Formalities
-- [ ] I have reviewed the [CONTRIBUTING.md](../CONTRIBUTING.md) file for detailed contributing guidelines.
+- [ ] I have reviewed the [CONTRIBUTING.md](https://github.com/openwrt/packages/blob/master/CONTRIBUTING.md) file for detailed contributing guidelines.
### If your PR contains a patch: