Update README.md: change website link to osmd.org

opensheetmusicdisplay.org is currently unavailable, so link to osmd.org for now

README.md

@@ -10,7 +10,7 @@
 [![Code Climate](https://codeclimate.com/github/opensheetmusicdisplay/opensheetmusicdisplay/badges/gpa.svg)](https://codeclimate.com/github/opensheetmusicdisplay/opensheetmusicdisplay)
 [![Commitizen friendly](https://img.shields.io/badge/commitizen-friendly-brightgreen.svg)](http://commitizen.github.io/cz-cli/)
 
-https://www.opensheetmusicdisplay.org/
+https://www.osmd.org/
 
 OpenSheetMusicDisplay renders MusicXML sheet music in the browser. It is the missing link between MusicXML and VexFlow. Built upon many years of experience in both sheet music interactivity and engraving, it is the perfect solution for app developers seeking to build digital sheet music services.