Fix a few small things in block/do documentation

lib/Language/control.pod

@@ -36,7 +36,7 @@ is by writing C<do> before it:
 Note that you need a space between the do and the block.
 
 The whole C<do {...}> evaluates to the final value of the block.  The block
-will be run when that value needed in order to evaluate the rest of the
+will be run when that value is needed in order to evaluate the rest of the
 expression.  So:
 
     False and do { 42.say };
@@ -51,7 +51,7 @@ In other words, it follows the same reification rules as everything else.
 
 Technically, C<do> is a loop which runs exactly one iteration.
 
-The C<do> may actually also be used on a statement (i.e. without brackets)
+A C<do> may actually also be used on a statement (without brackets)
 but this is mainly just useful for avoiding the syntactical need to
 parenthesize a statement if it is the last thing in an expression: