Add Platform to ecosystem

See https://github.com/7ojo/perl6-platform

Author: Jarkko Haapalainen

META.list

@@ -802,3 +802,4 @@ https://raw.githubusercontent.com/zoffixznet/perl6-WWW/master/META6.json
 https://raw.githubusercontent.com/araraloren/Net-FTPlib/7cee8a030084a9a3c03a696dc4a314d6ecc6d6d2/META6.json
 https://raw.githubusercontent.com/gfldex/perl6-proc-async-timeout/master/META6.json
 https://raw.githubusercontent.com/melezhik/sparrowdo-cpanm-github/master/META6.json
+https://raw.githubusercontent.com/7ojo/perl6-platform/master/META6.json