Readd temporary workaround for setting theme path
Readd temporary workaround for setting theme path

Setting the theme path via the `-t THEME` flag isn't recognized
and still requires to use the HUGO_THEME env variable as workaround.

See gohugoio/hugoThemes#412
See gohugoio/hugo#5061
See gohugoio/hugo#4851

spf13/hugoThemes,Nytoca/hugoThemes