Removed a forgotten paragraph in the readme that does no longer apply in the lib version.
Removed a forgotten paragraph in the readme that does no longer apply in the lib version.

filipstefansson/bootstrap-3-shortcodes,filipstefansson/bootstrap-3-shortcodes,robbieaverill/php-markdown,jockchou/php-markdown,ashur/php-markdown,Kapeli/php-markdown,queirozfcom/php-markdown-with-syntax-highlight,MWDelaney/bootstrap-3-shortcodes,nazar-pc/php-markdown-next,MWDelaney/bootstrap-3-shortcodes,MWDelaney/bootstrap-3-shortcodes,n054/php-markdown,mariokonrad/php-markdown