Add clarification about difference between component re-rendering and initial loading

Add a note that explains that the re-rendering loading states is a different concept from the components initial loading state regarding placeholders, with a link to the related "loading content" section in this doc

Author: Wertisdk

src/LiveComponent/doc/index.rst

@@ -998,6 +998,9 @@ Or, to *hide* an element while the component is loading:
     <!-- hide when the component is loading -->
     <span data-loading="hide">Saved!</span>
 
+Note that this is a different concept than showing a placeholder when initially loading the component itself.
+See :ref:`loading content <loading-content>` for more info.
+
 Adding and Removing Classes or Attributes
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~