bind: change data URI scheme format in pac flag usage

[Choraden]

'<' and '>' make a mess in sc docs.

-p, --pac <path or URL> (env FORWARDER_PAC)
    Proxy Auto-Configuration file to use for upstream proxy selection. It can be a local file or a URL, you can
    also use '-' to read from stdin. The data URI scheme is supported, the format is "data:base64,encoded_data".

[Choraden]

Looks like it also wasn't working in forwarder's docs, https://forwarder-proxy.io/cli/forwarder_run/#pac:

[mmatczuk]

So escape it.

[Choraden]

Escaped it. Notice, we also escape format in the first line '' as the first pair of backticks('`') is stripped in flag.UnquoteUsage(*flag.Flag).