README: add a note for existing user about lowercasing the parameters.
README: add a note for existing user about lowercasing the parameters.

mtn/cocoa-eh-hugo-theme,fuegowolf/cocoa-eh-hugo-theme,yeefom/cocoa-hugo-theme,huynle/cocoa-eh-hugo-theme,nishanths/cocoa-hugo-theme,lpancescu/cocoa-hugo-theme,pfitzseb/kakao