document that Lock is reentrant

Author: moritz

lib/Type/Lock.pod

@@ -17,7 +17,10 @@ I<critical section>).
     }
     say $x;         #
 
-High-level Perl 6 code should awoid the direct usage of locks, because they
+Locks are reentrant, that is, a thread that holds the lock can lock it again
+without blocking.
+
+High-level Perl 6 code should avoid the direct usage of locks, because they
 are not composable. Instead, high-level constructs such as
 L<Promise|/type/Promise>, L<Channel|/type/Channel> and Supply should be used
 whenever possible.