Update Block.pod6

Proper examples should go to /language/variables. I added the hint mostly to be able to link to the description of the Topic. I believe the Topic is quite an important topic and deserves more love. Just not here.

Author: gfldex

doc/Type/Block.pod6

@@ -10,8 +10,8 @@ A C<Block> is a code object meant for small-scale code reuse.  A block is
 created syntactically by a list of statements enclosed in curly braces.
 
 Without an explicit signature or placeholder arguments, a block has C<$_>
-as a positional argument. Which defaults to the outer scope's $_. Thus it
-will inherit the L<topic|/language/variables#index-entry-topic_variable> if possible.
+as a positional argument, which defaults to the outer scope's C<$_>. Thus it
+will inherit the L<topic|/language/variables#index-entry-topic_variable> if there is any.
 
     my $block = { uc $_; };
     say $block.^name;           # OUTPUT: «Block␤»