Update about.pod6 - fix broken CONTRIBUTING link

Author: ronaldxs

doc/Language/about.pod6

@@ -16,7 +16,7 @@ The official source for this documentation is located at L<perl6/doc on
 GitHub|https://github.com/perl6/doc>.
 
 The information in this particular document is a quick overview of the process
-described in more detail in L<CONTRIBUTING on GitHub|https://github.com/perl6/doc/CONTRIBUTING.md>.
+described in more detail in L<CONTRIBUTING on GitHub|https://github.com/perl6/doc/blob/master/CONTRIBUTING.md>.
 This document also provides a short introduction to writing the Perl 6
 POD files which produce the rendered pages in HTML or other formats.