Providing additional material for a paper in external source I have a short paper and there is a need to include additional material like figures, graphs, and tables. I want to keep the paper short. 

Is it acceptable to upload all the additional material on the external source (github or other), and to add a link with description in the paper?
Short answer: it depends on the publisher/conference organiser. 
Unless there is a strong reason not to, ask them. 

It is quite common to host additional material on a website.  Generally speaking, though, the paper should stand on its own, and any background reading and data visualisation should not be necessary to follow the narrative. Imagine an interested reader would want to see some more material after reading the paper, but not need it to understand everything. 

On the other hand, if there is no need for it at all, then it is best to not even refer to it - by referencing an online resource you commit to maintaining this, keeping the same URL and so on, and a strong, self-contained paper is always nicer.