Please add Installation instruction for mac

[Piyush Keshari]

Using Mac

1. Copy the code from the copy.xml file
2. Go to /Applications/MySQLWorkbench.app/Contents/Resources/data/code_editor.xml (to open the contents of the app right click on the workbench app and select 'Show Package Contents')
3. Open code_editor.xml
4. Paste the code you've selected before inside the tag <language name="SCLEX_MYSQL">, replacing all styles in that tag
5. Open your MySQL Workbench and be happy!

[Michael Caxias]

Thanks for contributting, here is the commit 0292a3e