DOC: add extra development section (#118)

* DOC: add extra development section

* Update docs/index.rst

Co-authored-by: sourcery-ai[bot] <58596630+sourcery-ai[bot]@users.noreply.github.com>

---------

Co-authored-by: sourcery-ai[bot] <58596630+sourcery-ai[bot]@users.noreply.github.com>

docs/index.rst

@@ -6,10 +6,8 @@
 
     install
     usage
-    contributing
-    changelog
 
-.. Warning: then usage of genindex is a hack to get a TOC entry, see
+.. Warning: the usage of genindex is a hack to get a TOC entry, see
 .. https://stackoverflow.com/a/42310803. This might break the usage of sphinx if
 .. you want to create something different than HTML output.
 .. toctree::
@@ -18,3 +16,10 @@
 
     api/opensmile
     genindex
+
+.. toctree::
+    :caption: Development
+    :hidden:
+
+    contributing
+    changelog