(DOCSP-11333) Display document count in left navigation panel (mongodb#22)

* (DOCSP-11333) Display document count in left navigation panel

* Specify left nav panel

* Update from copy review

Author: zach-carr

source/databases-collections.txt

@@ -45,6 +45,10 @@ Click a collection to view its documents, schema, and indexes.
 Documents
 ``````````
 
+When you expand a collection, |vsce| displays that collection's 
+document count next to the :guilabel:`Documents` label in the 
+navigation panel.
+
 When you expand a collection's documents, |vsce| lists the ``_id`` of
 each document in the collection. Click an ``_id`` value to open that
 document in VS Code and view its contents.