Add learnings from Trenitalia invoices feature

[marcoow]

• ask more questions when coming into a story to get a better understanding of the story you're now helping with or reviewing a PR for
• pair more, look for pairing opportunities early on: a second pair of eyes can be helpful to come up with a better strategy for how to implement a feature and pairing can also be more effective than splitting up a story and working on multiple aspects in parallel (in which case you run into situations where people work on the same stuff redundantly, depend on each other etc.)
• plan everything thoroughly: make sure all info/api etc. we need to work on something is available when we start the work; make sure a story is well understood, implications are well understood, the size of a story is well understood etc.
• the team needs to review pre-planned stories before sprint planning so that wrong estimates, missing todos etc. are identified early
• use feature flags to be able to merge big stories incrementally without affecting production users; this allows splitting up things into smaller units that can be merged/released individually without even being fully functional

[marcoow]

@jessica-jordan, @geekygrappler, @pangratz: anything missing?

[pangratz]

LGTM

[jayjayjpg]

The sum up also sounds good to me, thank you for wrapping this up @marcoow

[marcoow]

I'm closing this as all of the above points are addressed in the playbook now.