add wiki for mvmplaceholders

[leoncp9]

i see placeholders for featherboard at plotsuared 5
https://wiki.intellectualsites.com/plotsquared/placeholders
they don't work
like {plotsquared_plot_count}
where are th wiki of the mvmplaceholders list

[Citymonstret]

We only support PlaceholderAPI, but you can use that format and it should work.

[leoncp9]

{placeholderapi_plotsquared_members}
{placeholderapi_plotsquared__xy}
this two placeholders don't show nothing at featherboard plugin
proof:
https://prnt.sc/sin4nh

[Citymonstret]

Those are not valid placeholders. Take another look at the wiki.