Review & update model source links

[QuinnHe]

For instance, "The ml5.js image classifier is based on the MobileNet, Darknet, and DoodleNet." We need to go over each model, and check whether the source link is correct.

[shiffman]

I wonder if something like this would be more accurate?

The ml5.js image classifier uses the pre-trained MobileNet model by default. You can optionally load and use other models such as Darknet as well as a custom-trained model, DoodleNet, which is also built upon the MobileNet architecture and trained on images from the Google Quick, Draw dataset.

[QuinnHe]

To-do
As Dan mentioned above, go through all model sources, and provide a bit more detailed info.