add info about default perspective (#572)

modules/ROOT/pages/explore/explore-perspectives/perspective-creation.adoc

@@ -3,6 +3,13 @@
 [[perspective-creation]]
 = Creation and use
 
+== Default Perspective
+
+When you connect Explore for the first time to a non-empty database, a Perspective is automatically created for you (see *Generate Perspective* below for details on how this is done.).
+This is called *Default Perspective* and it cannot be modified from the UI.
+However, if there are changes to the database, Explore updates the Default Perspective accordingly.
+If you want to customize the view, you can create a new Perspective.
+
 == Creating a Perspective
 
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