add mzmine 3 documentation link
<!-- HELP -->
<Menu text="Help">
<MenuItem text="About MZmine" onAction="#showAbout"/>
- <MenuItem text="Tutorials" onAction="#openLink"
+ <MenuItem text="Open documentation (MZmine 3)" onAction="#openLink"
+ userData="https://mzmine.github.io/mzmine_documentation/"/>
+ <MenuItem text="Open documentation (MZmine 2)" onAction="#openLink"
userData="http://mzmine.github.io/documentation.html"/>
<MenuItem text="Support" onAction="#openLink"
userData="http://mzmine.github.io/support.html"/>
