Add DNSMASQ_LISTENING=bind to README.md

[loeffelpan]

Description

Adding missing option bind for DNSMASQ_LISTENING.

Motivation and Context

See https://discourse.pi-hole.net/t/dnsmasq-listening-setting-for-binding-single-interface/71417/6

How Has This Been Tested?

Tested the additional bind option in my production environment.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation change/addition

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/dnsmasq-listening-setting-for-binding-single-interface/71417/7

[yubiuser]

You need to sign-off your commit https://docs.pi-hole.net/guides/github/how-to-signoff/

[rdwebdesign]

Note:

I don't think we need a new image tag when this is merged because this only changes the README file.