Add link to documentation

documentation/index_vm.html

@@ -11,6 +11,10 @@ <h2>Introduction</h2>
 
 <p>PEcAn is not itself an ecosystem model, and it can be used to with a variety of different ecosystem models; integrating a model involves writing a wrapper to convert inputs and outputs to and from the standards used by PEcAn. Currently, PEcAn supports the Ecosystem Demography model (ED2, Medvigy et al 2009), SIPNET (Sacks et al., 2005), and BioCro (Miguez et al, 2012). </p>
 
+<h2>Documentation</h2>
+
+The documentation for PEcAn is kept in GitBook. A PDF version can be found <a href="pecan.pdf">locally</a>. The most up to date version can be found at <a href="https://pecan.gitbooks.io/pecan-documentation/content/">GitBook</a>.
+
 <h2>Demonstration</h2>
 
 <p>This system allows you to <a href="/pecan/">experiment and create simulations</a> using  PEcAn, ED, SIPNET, BioCro and BETYdb. The first page will allow for selection of a site where the simulation will run at. The <a href="/bety/">BETY database</a> contains data for both the local system as well as data on the illinois ebi servers (ebi-cluster and ebi-forecast). Only those sites with data on the local system can be run. After selecting a site and entering the date range for the simulation, PEcAn will take over and set up and execute the selected model. Once the model is finished it will allow you to create graphs with the results of the simulation as well as download the results. It is also possible to see all <a href="/pecan/history.php">past experiments and simulations</a>.</p>