Added Operating System :: RISC OS (#32)

* Added Operating System :: RISC OS

* Moved 'Operating System :: RISC OS' to the right place.

Co-authored-by: Dustin Ingram <di@users.noreply.github.com>

Author: c-jo

trove_classifiers/__init__.py

@@ -347,6 +347,7 @@
     "Operating System :: POSIX :: SCO",
     "Operating System :: POSIX :: SunOS/Solaris",
     "Operating System :: PalmOS",
+    "Operating System :: RISC OS",
     "Operating System :: Unix",
     "Operating System :: iOS",
     "Programming Language :: APL",