reorg repo structure and modify PR template (#21)

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,9 +1,13 @@
-Before submitting a Jupyter notebook, follow this mandatory checklist:
+If you are opening a PR for `Notebooks`, follow this mandatory checklist:
 
 - [ ] Use the [notebook template](https://github.com/GoogleCloudPlatform/vertex-ai-samples/blob/master/notebooks/notebook_template.ipynb) as a starting point.
 - [ ] Follow the style and grammar rules outlined in the above notebook template.
 - [ ] Verify the notebook runs successfully in Colab since the automated tests cannot guarantee this even when it passes.
 - [ ] Passes all the required automated checks
 - [ ] You have consulted with a tech writer to see if tech writer review is necessary. If so, the notebook has been reviewed by a tech writer, and they have approved it.
-- [ ] This notebook has been added to the CODEOWNERS file, pointing to the author or the author's team. If the CODEOWNERS file doesn't exist, create one in the nearest folder that makes sense.
+- [ ] This notebook has been added to the [CODEOWNERS](https://github.com/GoogleCloudPlatform/vertex-ai-samples/blob/master/docs/CODEOWNERS) file, pointing to the author or the author's team.
 - [ ] The Jupyter notebook cleans up any artifacts it has created (datasets, ML models, endpoints, etc) so as not to eat up unnecessary resources.
+
+If you are opening a PR for `Community Content`, follow:
+
+- [ ] This Community Content has been added to the [CODEOWNERS](https://github.com/GoogleCloudPlatform/vertex-ai-samples/blob/master/docs/CODEOWNERS) file, pointing to the author or the author's team. 

tutorials/community/README.md

@@ -1,4 +0,0 @@
-# Google Cloud Vertex AI Community Tutorials
-
-## Disclaimer
-The community tutorials are not officially maintained by Google. 

tutorials/official/README.md

@@ -1,4 +0,0 @@
-# Google Cloud Vertex AI Official Tutorials
-
-The official tutorials are organized by Google Cloud Vertex AI products.
-