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)
• [x] Documentation change/addition

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] 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]

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