docs: add info on draft pull requests for work of longer duration

Author: ringods

.github/CONTRIBUTING.md

@@ -37,6 +37,7 @@ This ensures that any changes you've made will still result in a clean and funct
 
 * _ALWAYS_ submit pull requests against the [dev branch](https://github.com/pattern-lab/patternlab-node/tree/dev). If this does not occur, I will first, try to redirect you gently, second, attempt to redirect the target branch myself, thirdly, port over your contribution manually if time allows, and/or lastly, close your pull request. If you have a major feature to stabilize over time, talk to @bmuenzenmeyer via an issue about making a dedicated `feature-branch`
 * Keep your pull requests concise and limited to **ONE** substantive change at a time. This makes reviewing and testing so much easier.
+* If it takes you considerable time to finish your work, submit a [draft pull request](https://github.blog/2019-02-14-introducing-draft-pull-requests/). This is Github's way to indicate work in progress but allows for feedback.
 * Commits should reference the issue you are adressing. For any Pull Request that you send, use the template provided.
 * Commits are best formatted using the [conventional commits pattern](https://conventionalcommits.org/).
 * If you can, add some unit tests using the existing patterns in the `.packages/core/test` directory