GlobalStyles docs & performance

[esso23]

https://blazorstyled.io/globalStyles
@Styled.GlobalStyles["ColorHotPink"] no longer available in v3.
Should be replaced with @Styled.GetGlobalStyle("ColorHotPink")

Edit: Also it's extremely slow (somewhere between 5x to 10x slower) compared to previous version and does not work very reliably (sometimes it's like styles weren't even loaded).

[chanan]

I haven't been able to update the docs site due to: #102