Fixes some grammar around error

Mainly to close #1769; also closes #1776 which was a duplicate.

Author: JJ

doc/Language/syntax.pod6

@@ -150,7 +150,7 @@ say "world";
 
 =head2 Comments
 
-Comments are parts of the program text only intended for human readers, and
+Comments are parts of the program text which are only intended for human readers;
 the Perl 6 compilers do not evaluate them as program text.
 
 Comments count as whitespace in places where the absence or presence of