Google Docs integrates with Google Sites allowing you to create a Google Doc and display it on a Sites page. The process is pretty much the same as inserting other elements on a Sites page.
Document with height set at 300px
Document with height set at 600px (the default)
Document with height set at 1000px
Height is probably the key element to consider as this determines how much space the document will take up on the page. If you make this too small, then users will only see a small amount of the doc at one time and will need to scroll a lot to read the rest. If you make it too big then your Site page will become very large. You may need to experiment to get the right setting as this will vary depending on the content of the page, the length of the document and the layout of the page.
I've added a document in the right column with 3 different height settings as an example.