relabel api headers

Author: asinghvi17

docs/src/api.md

@@ -1,13 +1,15 @@
 # API Reference
 
+## Exports
+
 ```@autodocs
 Modules = [GeometryBasics]
 Order   = [:module, :constant, :type, :function, :macro]
 Public  = true
 Private = false
 ```
 
-## What isn't
+## Private
 
 ```@autodocs
 Modules = [GeometryBasics]