Add a little explanation

doc/Language/control.pod6

@@ -178,7 +178,7 @@ If the code inside the block has not finished, the call to C<.result> will
 wait until it is done.
 
 A C<start> may also be used on a bare statement (without curly braces).
-This is mainly just useful when calling a subroutine / method on an object
+This is mainly useful when calling a subroutine / method on an object
 is the only thing to do asynchronously.
 
     sub get42 { 42 }
@@ -187,7 +187,8 @@ is the only thing to do asynchronously.
 
 Note that code executed this way does not have access to the special
 variables L«C<$!>|/syntax/$!» and L«C<$/>|/syntax/$/» of its outer
-block, but receives new ones.
+block, but receives new ones, so every asynchronous task has its
+per-task state.
 
 Thus, C<try> expressions and regex matches executed in the
 asynchronous task have their per-task state.