Removed outdated remark in readme about being bundled with WordPress default installs.
Removed outdated remark in readme about being bundled with WordPress default installs.

TypeFriendly/PHP-Markdown,mariokonrad/php-markdown,jockchou/php-markdown,c9s/php-markdown,n054/php-markdown,MWDelaney/bootstrap-3-shortcodes,alganet/ElephantMarkdown,queirozfcom/php-markdown-with-syntax-highlight,MWDelaney/bootstrap-3-shortcodes,filipstefansson/bootstrap-3-shortcodes,filipstefansson/bootstrap-3-shortcodes,Kapeli/php-markdown,robbieaverill/php-markdown,nazar-pc/php-markdown-next,ashur/php-markdown,itafroma/php-markdown,MWDelaney/bootstrap-3-shortcodes,drosenstark/php-markdown