Fix typo in documentation for Terraform CIDR Subnets Module.

[HecticSerenity]

The text

baz has a new_bits of 8, so its final prefix length is only 8 + 4 = 12 bits.
                      ^

is incorrect. baz has new_bits of 4 and this text contains an '8' (see caret). (The equation correctly shows 4 for baz's new_bits)

The input for baz is:

    {
      name     = "baz"
      new_bits = 4
    }

see cidr module documentation

[Hanse00]

It's worth noting that the README of this repo does have the correct text:

terraform-cidr-subnets/README.md

Line 56 in 2a772a8

is 8 + 8 = 16. `baz` has a `new_bits` of 4, so its final prefix length is

Perhaps the docs website just isn't in sync with the readme for some reason?