Re-word spec faq

Fixes #772

Author: coke

doc/Language/faq.pod6

@@ -66,11 +66,16 @@ Google is often outdated.
 You could also try searching the Freenode #perl6 IRC channel log via
 L<Google|https://www.google.co.uk/search?q=site:irclog.perlgeek.de+inurl:perl6>
 
-=head2 What is the Perl 6 spec?
+=head2 What is the Perl 6 specification?
 
-The "spec" refers to the official test suite for Perl 6.  It's called
-roast and L<hosted on github|https://github.com/perl6/roast>. It
-is the measure of how complete a Perl 6 implementation is.
+The specification refers to the official test suite for Perl 6.  It's called
+roast and is L<hosted on github|https://github.com/perl6/roast>. Any compiler
+that passes the tests is considered to implement that version of the Perl 6
+specification.
+
+Roast's master branch corresponds to the latest development that isn't
+necessarily part of any specification yet, and has other branches that
+correspond to specific versions, e.g. "6c.errata".
 
 =head2 Is there a glossary of Perl 6 related terms?