message: Add TinyXML2 to NOTICE file
diff: @@ -30,3 +30,4 @@ license files. These software products and their licenses are as follows:
  * Gecko (general/gecko.{cpp,hpp}) -- BSD 3-clause license
  * Picojson (fem/picojson.h) -- Custom 2-clause license
  * Zstr (general/zstr.hpp) -- MIT license
  +* TinyXML2 (general/tinyxml2.{cpp,h}) -- zlib license
  