Configuration reference: provider options environment example missing binary

[NitrogenUA]

Lexicon binary is missing in the "Passing provider options to Lexicon" environment variable example.

While we're at it, I couldn't get --config-dir to work in the trailing position as given in "provider options" -> "configuration file" example. Usage message for lexicon suggests that optional parameters should go first followed by the actual DNS manipulation command. Otherwise argument processing seems to break in my experience. However I have not looked through the code to confirm this beyond doubt. Should we move it forward like so?
lexicon --config-dir /path/to/config cloudflare create domain.net TXT --name foo --content bar
It might appear as a minor thing, but it did cost me additional headbashing in conjuction with the typo from #1431 since I had BOTH parameter placement in lexicon invocation AND yml-configuration wrong! 😕
Hopefully this suggested change can save some time for other users.

[adferrand]

Thanks for the fix.

Indeed there is something not obvious regarding --config-file. The thing that there are two args parsing level. The first one is related to general options to Lexicon, including the actual provider. Then based on the selected provider, the options related to the provider itself are parsed. So effectively, options related to Lexicon should come first, ending with the provider name, then comes the DNS action + the provider options.

You're example lexicon --config-dir /path/to/config cloudflare create domain.net TXT --name foo --content bar is the right one.

I have in my backlog a redesign of the argument parsing system to avoid this limitation and permit to pass the arguments in any order.

[adferrand]

I fix the documentation regarding options as a follow-up to your PR.