Pull request to fix rdnc-addzone doc

Summary

Stray $ and \ in man page for rdnc in the addzone section

BIND version used

main

Steps to reproduce

1. Visit https://bind9.readthedocs.io/en/latest/manpages.html#rndc-name-server-control-utility
2. Read until one gets to the addzone section
3. See $ \ ...
4. Wonder what the \ is doing.

What is the current bug behavior?

There's a $ which could be a shell prompt hint, but is inconsistent with the rest of the docs, and there's a \, and I have no idea what it's for, but it's wrong.

What is the expected correct behavior?

Neither $ nor \

Relevant configuration files

N/A (well, I suppose whatever the defaults are for readthedocs)

Relevant logs and/or screenshots

Possible fixes

PR: https://github.com/jsoref/bind9/tree/rdnc-addzone

n.b. GitLab won't let me fork this repository, so... I forked it in GitHub.