Add placeholder folders for examples which are in other branches.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4789 dfc29bdd-3216-0410-991c-e03cc46cb475

examples/27.HelloWorld_Android/where_is_it.txt

+This example is currently only available in Irrlicht svn branch for ogl-es: https://sourceforge.net/p/irrlicht/code/HEAD/tree/branches/ogl-es
+It will be merged with the svn trunk at some point in the future.

examples/28.HelloWorld_iPhone/where_is_it.txt

+This example is currently only available in Irrlicht svn branch for ogl-es: https://sourceforge.net/p/irrlicht/code/HEAD/tree/branches/ogl-es
+It will be merged with the svn trunk at some point in the future.

examples/29.HardwareSkinning/where_is_it.txt

+This example is currently only available in Irrlicht svn branch for the shader-pipeline: https://sourceforge.net/p/irrlicht/code/HEAD/tree/branches/shader-pipeline
+It will be merged with the svn trunk at some point in the future.