add hackmd

README.md

@@ -850,6 +850,7 @@ See https://github.com/n1trux/awesome-sysadmin#monitoring and https://github.com
 *See also [Wikis](#wikis)*
 
   * [dillinger](http://dillinger.io/) - The last Markdown editor, ever. ([Source Code](https://github.com/joemccann/dillinger/)) `MIT` `Nodejs`
+  * [HackMD](https://www.hackmd.io) - Realtime collaborative markdown notes on all platforms. `MIT`  `Node.js`
   * [Laverna](https://laverna.cc/) - Laverna is a Javascript note taking application with Markdown editor and encryption support. Consider it like open source alternative to Evernote. ([Demo](https://laverna.cc/index.html#notes), [Source Code](https://github.com/Laverna/laverna)) `MPLv2` `Nodejs`
   * [Leanote](http://leanote.org/) - Leanote, Not Just A Notepad! Open source cloud notepad. ([Demo](https://leanote.com/note), [Source Code](https://github.com/leanote/leanote)) `GPLv2` `Go`
   * [Markdown Edit](http://georgeosddev.github.com/markdown-edit/) - Online markdown editor/viewer. ([Source Code](https://github.com/georgeOsdDev/markdown-edit)) `MIT` `HTML5`