At this time it's not possible because Google Docs doesn't have built-in features to embed external content.
There are features to insert external content like the Insert menu, the Research tool, and add-ons but they are not able to "link" content. The insert an image, insert a drawing, insert a copy of the selected content; the research tool could insert link to a web page, a copy of text or of a image, but not to embed them in the way that an IFRAME works in a webpage or a gadget/widget in a web page or a sharing tool like Google+ among others.
References from the Google Docs Help Center
Insert an image
Insert a drawing