Here are the steps to put a link onto the Start page which will start the GApp Docs:

1)   Login into the Control panel, click on the Start Page link then on the Customize link
2)   Click on the Content tab and then click on Add Stuff
3)   Click on Create custom content
4)   Choose: Static, text, images, and links
5)   Fill in the Section Name if asked and click on Edit HTML (Don't
click on add link)
6)   Clear the edit screen and add the following line of code. My docs
7)   Click on Update button
8)   Click on Create Section
9)   Click on Add it now for this new widget
10) Click on Publish then Publish Updates on the next page
11) Click on Preview then on Add stuff => Add it now  NEEDS WORK
12) Each account holder can add this to their Start page. It will be visible already on start.mydomain.com.

This assumed that the CNAMES for docs and start have been created.

This is very bare bones obviously but it will allow you to start up
Documents for the domain from your start page.