*Issue #, if available:*

*Description of changes:*


By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.

---------

Co-authored-by: Xiang Song <[email protected]>

*Issue #, if available:*

*Description of changes:*
This PR fix the type error of `reverse_edge_types_map` in the API
example notebook 2. When it should be a dictionary. When set the
`exclude_training_targets` to be `True`, this map will be used.

By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.

Co-authored-by: Ubuntu <[email protected]>

*Issue #, if available:*
#789 

*Description of changes:*
Add doc for multi-task learning.


By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.

---------

Co-authored-by: Xiang Song <[email protected]>