Update example ZapAddOn.xml with a helpset (#1656)
Update example ZapAddOn.xml with a helpset (#1656)

Add example on how to declare a helpset.

Part of zaproxy/zaproxy#3734 - Allow add-ons without extensions to have
help pages
secdec/zap-extensions,thc202/zap-extensions,denniskniep/zap-extensions,zapbot/zap-extensions,psiinon/zap-extensions,zapbot/zap-extensions,zapbot/zap-extensions,kingthorin/zap-extensions,secdec/zap-extensions,veggiespam/zap-extensions,zapbot/zap-extensions,psiinon/zap-extensions,denniskniep/zap-extensions,veggiespam/zap-extensions,zaproxy/zap-extensions,kingthorin/zap-extensions,veggiespam/zap-extensions,denniskniep/zap-extensions,kingthorin/zap-extensions,veggiespam/zap-extensions,thc202/zap-extensions,veggiespam/zap-extensions,psiinon/zap-extensions,zaproxy/zap-extensions,denniskniep/zap-extensions,psiinon/zap-extensions,secdec/zap-extensions,thc202/zap-extensions,denniskniep/zap-extensions,thc202/zap-extensions,kingthorin/zap-extensions,kingthorin/zap-extensions,secdec/zap-extensions,zapbot/zap-extensions,zaproxy/zap-extensions,zapbot/zap-extensions,kingthorin/zap-extensions,secdec/zap-extensions,secdec/zap-extensions,zaproxy/zap-extensions,psiinon/zap-extensions,psiinon/zap-extensions,thc202/zap-extensions,thc202/zap-extensions,zaproxy/zap-extensions,secdec/zap-extensions,zaproxy/zap-extensions,veggiespam/zap-extensions,denniskniep/zap-extensions