Attempt to write some docs for Pair.freeze - perhaps more text is needed

gistfile1.txt

=head2 method freeze

Defined as:

    method freeze(Pair:D:)

Usage:

    PAIR.freeze

Makes the value of the C<Pair> read-only, by removing it from its Scalar container, and returns it.

    my $str = "apple";
    my $p = Pair.new('key', $str);
    $p.value = "orange";              # this works as expected
    $p.say;                           # key => orange
    $p.freeze.say;                    # orange
    $p.value = "a new apple";         # Fails with 'Cannot modify an immutable Str'