Adds sub as suggested to close #2393

doc/Type/Scalar.pod6

@@ -87,7 +87,7 @@ variables.
     CATCH { default { put .^name, ': ', .Str } };
     # OUTPUT: «X::Assignment::RO: Cannot modify an immutable Int␤»
 
-=head1 Atomic Operations on Scalar
+=head1 Atomic operations on Scalar
 
 A C<Scalar> can have its value changed using a hardware-supported atomic
 compare and swap operation. This is useful when implementing lock free data
@@ -157,7 +157,7 @@ Example:
 
 =head1 Routines
 
-=head2 atomic-assign
+=head2 sub atomic-assign
 
 Defined as:
 
@@ -167,7 +167,7 @@ Performs an atomic assignment of C<$value> into the C<Scalar> C<$target>. The
 C<atomic-assign> routine ensures that any required barriers are performed such
 that the changed value will be "published" to other threads.
 
-=head2 atomic-fetch
+=head2 sub atomic-fetch
 
     multi sub atomic-fetch($target is rw)
 
@@ -191,7 +191,7 @@ It would be legal for a compiler to observe that C<$started> is not updated in
 the loop, and so lift the read out of the loop, thus causing the program to
 never terminate.
 
-=head2 cas
+=head2 sub cas
 
 Defined as: