mention unit is new scope declarator

Author: TimToady

S02-bits.pod

@@ -2013,6 +2013,7 @@ Normal names and variables are declared using a I<scope declarator>:
     state       # introduces lexically scoped but persistent names
     augment     # adds definitions to an existing name
     supersede   # replaces definitions of an existing name
+    unit        # like our, but introduces a compilation-unit scoped name
 
 Names may also be declared in the signature of a function.  These are
 equivalent to a C<my> declaration inside the block of the function, except