add a link to `Beatmap search` wiki article in the beatmap search page

[Hiviexd]

this wiki page has a wealth of information about very useful search filters, yet it's completely hidden without any outside references. it'd be really great if the beatmap listing search has a link to that article in order to make users aware of these filters.

this also matches how the bbcode editor links to its respective wiki page.

[vmfunc]

where to show it though?

these would be the two places i have in mind.

[cl8n]

since it's related only to what you can put in the search bar, I think it should be near there instead. maybe directly left of search icon?