Add link to Run2OperationSummary twiki

[rmatev]

We should probably add a link to https://twiki.cern.ch/twiki/bin/viewauth/LHCbInternal/Run2OperationSummary, which is the canonical place for listing know issues with the Run 2 data, and is potentially interesting for analysts. Where is this best done?

[alexpearce]

I'd say "Asking good questions" could work (as this page can help answer "what could be/is wrong with my data?") or perhaps "Changes to the data flow in Run 2".