Extending Doc: Add warning about what the Qt Creator plugin wizard creates

Because we do not guarantee any source or binary compatibility,
you should use the Qt Creator version that you want to develop for
to create the plugin

Change-Id: I747653f8bbd3df9cc82af7fac67abcf14e786241
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>

doc/api/first-plugin.qdoc

@@ -35,6 +35,12 @@
     build and use one for actually developing, and the other for testing
     your plugin with.
 
+    You need to make sure that you use the same \QC version that you want
+    to develop for to create the plugin. Because of the
+    \l{Binary and Source Compatibility} rules of \QC, the \QC plugin wizard
+    creates a plugin that might only compile and run with the same \QC
+    version that it was created with.
+
     \list 1
         \li Select \gui{File > New File or Project > Libraries > Qt Creator Plugin > Choose}.