link to MacOS ticket from readme

fixes scala#1150

Author: SethTisue

README.md

@@ -12,6 +12,8 @@ To build and view the site locally:
     bundle install
     bundle exec jekyll serve -I
 
+([Trouble on MacOS?](https://github.com/scala/docs.scala-lang/issues/1150))
+
 For more details, read on.
 
 ## Quickstart with Docker ##