add html-to-markdown (avelino#3200)

* add html-to-markdown to README.md

* change order slightly

README.md

@@ -1749,6 +1749,7 @@ See [go-hardware](https://github.com/rakyll/go-hardware) for a comprehensive lis
     * [goribot](https://github.com/zhshch2002/goribot) - A simple golang spider/scraping framework,build a spider in 3 lines.
     * [gotext](https://github.com/leonelquinteros/gotext) - GNU gettext utilities for Go.
     * [guesslanguage](https://github.com/endeveit/guesslanguage) - Functions to determine the natural language of a unicode text.
+    * [html-to-markdown](https://github.com/JohannesKaufmann/html-to-markdown) - Convert HTML to Markdown. Even works with entire websites and can be extended through rules.
     * [htmlquery](https://github.com/antchfx/htmlquery) - An XPath query package for HTML, lets you extract data or evaluate from HTML documents by an XPath expression.
     * [inject](https://github.com/facebookgo/inject) - Package inject provides a reflect based injector.
     * [ltsv](https://github.com/Wing924/ltsv) - High performance [LTSV (Labeled Tab Separated Value)](http://ltsv.org/) reader for Go.