Update the Project section of the docs

docs/source/int_glossary.rst

@@ -9,13 +9,19 @@ Glossary
    Root Folder
       A "Root Folder" is a top level folder of the project tree in novelWriter. Each type of root
       folder has a specific icon to identify it. For an overview of available root folder types,
-      see :ref:``
+      see :ref:`a_proj_roots`.
 
    Novel Documents
-      These are documents that are created under a "Novel" :term:`root folder`.
+      These are documents that are created under a "Novel" :term:`root folder`. They behave
+      differently than :term:`Project Notes`, and have some more restrictions. For instance, they
+      can not exist in folders intended only for project notes. See the :ref:`a_struct` chapter for
+      more details.
 
    Project Notes
-      ...
+      Project Notes are unrestricted documents that can be placed anywhere in your project. You
+      should not use these documents for story elements, only for notes. Project notes are the
+      source files used by the Tags and References system. See the :ref:`a_references` chapter for
+      more details on how to use them.
 
    Tag
       ...
@@ -28,3 +34,12 @@ Glossary
 
    Context Menu
       ...
+
+   Headings
+      Each level of headings in :term:`Novel Documents` have a specific meaning in terms of the
+      structure of the story. That is, they determine what novelWriter considers a partition, a
+      chapter, a scene or a text section. For :term:`Project Notes`, the header levels don't
+      matter. For more details on headings in novel documents, see :ref:`a_struct_heads`.
+
+   Keyword
+      ...