Update godot_design_philosophy.rst

I am suggesting a small addition to the sentence as it was unclear to me at first whether the external program needs a plugin or the plugin needs to available to Godot.  I take it the latter is true?

getting_started/introduction/godot_design_philosophy.rst

@@ -78,7 +78,7 @@ the ability to hot-reload locally and on remote devices, etc.
 
 The goal is to offer a full package to create games and a continuous
 user experience. You can still work with external programs as long as
-there is an import plugin for it. Or you can create one, like the `Tiled
+there is an import plugin available in Godot for it. Or you can create one, like the `Tiled
 Map Importer <https://github.com/vnen/godot-tiled-importer>`__.
 
 That is also partly why Godot offers its own programming language