[OnlineHelp] Add example to Verifiable Secret Sharing

[tassadarius]

The online help of the plugin Verifiable Secret Sharing (org.jcryptool.visual.vss) lacks an example with calculation steps in the online help. The similar plug-in Shamir's Secret Sharing has one.

Where: org.jcryptool.visual.verifiablesecretsharing/nl/{de,en}/help/content/vssAlgorithm.html

There should be placeholders indicating the position:

  <!-- 
  TODO #365: Add calculation example here
-->

Also, some variables within the formulas are not explained properly (e.g. N in equation 5).