Update doc to suggest using () instead of ; when using <Plug> mappings

[Aster89]

I'm attempting to gather consensus and, if gathered, apply an improvement to the doc as regards the suggestion - found at :help using-<Plug> - of using the ; terminator; the doc should instead suggest to use (-) delimiters.

The matter surfaced on vi.stackexchange, see @romainl 's answer and N.W.'s comment.

[chrisbra]

I think this makes sense, thanks

[romainl]

What I meant to say in the linked answer was that what comes after <Plug> is 100% arbitrary. It doesn't have to be in PascalCase. It doesn't have to end with a "terminator". It doesn't have to be wrapped in parentheses or anything. It doesn't have to be legible or short or make any kind of sense. It's just whatever the person who create that mapping came up with.

Using a specific "terminator", wrapping the name in a pair or characters, using PascalCase to separate the plugin name from the functionality… it's all just tricks.

And I think that the doc could be a little bit more transparent about that.

[chrisbra]

I made it a bit more clear