[io grant] Document IO::Handle.nl-in

doc/Type/IO/Handle.pod6

@@ -530,6 +530,28 @@ This returns a value that the operating system would understand as a "file descr
 is suitable for passing to a native function that requires a file descriptor as an
 argument such as C<fcntl> or C<ioctl>.
 
+=head2 method .nl-in
+
+Defined as:
+
+    method nl-in(--> Proxy:D) is rw
+
+One of the attributes that can be set via C<.new>.
+Defaults to C<["\x0A", "\r\n"]>
+Takes either a L<Str> or L<Array> of C<Str> specifying line ending(s) for this
+handle. If C<.chomp> attribute is set to C<True>, will strip these endings
+in routines that C<chomp>, such as L«C<get>|/routine/get» and
+L«C<lines>|/routine/lines».
+
+=begin code :skip-test
+    with 'test'.IO {
+        .spurt: '1foo2bar3foo'; # write some data into our test file
+        my $fh will leave {.close} = .open; # can also set .nl-in via .open arg
+        $fh.nl-in = [<foo bar>]; # set two possible line endings to use;
+        $fh.lines.say; # OUTPUT: ("1", "2", "3").Seq
+    }
+=end code
+
 =head2 method opened
 
 Defined as: