toc collapse issue

* still trying to fix toc collapse, moved toc_depth to pdf_book
*also attempting to add a link back to main website

index.Rmd

@@ -22,8 +22,8 @@ header-includes:
 output:
   bookdown::pdf_book:
     template: null
-  bookdown::gitbook:
     toc_depth: 4
+  bookdown::gitbook:
     includes:
       in_header: [google_analytics.html]
     split_by: rmd
@@ -33,6 +33,7 @@ output:
         collapse: none
         before: |
           <li><a href="/">The OBIS manual</a></li>
+          <li><a href="/">[The OBIS.org](https://obis.org/)</a></li>
 documentclass: book
 biblio-style: apalike
 link-citations: yes
@@ -44,6 +45,7 @@ editor_options:
 
 ![](images/obis_logo.png){width=50%}
 
+
 # Introduction
 
 This manual provides an overview on how to contribute data to OBIS and how to acess data from OBIS. It provides guidelines for OBIS nodes and data providers on the OBIS standards and data management best practices to ensure that data published via OBIS are of high quality and follows internationally recognised standards. It also provides guidelines for data users on how to access, process and visualize data from OBIS.