title: Maven site documentation: Add links to additional documents
body: <p>I want to generate project documentations with the Maven site plugin. The default layout, structure and functions with "Project Information" and "Project Reports" is ok for me. 
  But I want to add an additional (third) section "Additional Documentation", which links to some more documents, if there are such documents in the project. </p>
  
  <p>I can create a directory  <code>src/site/resources/otherDocu</code> and the documents will be copied to the  <code>target/site/otherDocu</code>  directory, as desired. However, the generated site does not link to them. </p>
  
  <p>I would like a third section "Additional Documentation", which lists and links the files in the mentioned directory. I want to do this with as small an overhead as possible. Specifically, if it can be avoided, I do not want to include an own <code>site.xml</code>, along with css etc. as described in many solutions. How can I use the default site configuration and only "inject" a part? Or, if this is the only way, it should be possible to configure a file (say <code>site.xml</code>) only once in a parent POM and inherit it for all other projects. How can I make it list the files found in <code>src/site/resources/otherDocu</code> and display links to them?</p>
  
  <p>Or, what I also was thinking of: I could write an own report plugin, which does this, and then I only need to specify this plugin in the "reporting / plugins" section in the POM, as I did for the other reporting plugins. With this solution, I could probably create an additional entry in the "Project Reports" section, like for every other reporting plugin, which is a step in the correct direction. But I need several entries (because of several linked documents), or one entry "Additional docu" with sub-entries. </p>
  
  <p>Which way is the easier to go? Does you have a recommendation or a similar solution? Does anyone have a file (<code>site.xml</code> or similar) which already does some listing, does not need all other resources (images etc.) and can be inherited? </p>