(Railsの)appの場合には: sorbet/rbi/shims/app と言った感じで。
When rbi-central does not have RBI files for a gem, tapioca init will still have created some autogenerated RBI files for that gem. These autogenerated files are a great way to start off writing hand-written RBIs for a gem! Simply copy the autogenerated file from the sorbet/rbi/gems/ folder to sorbet/rbi/shims/gems, and start modifying it by hand.
A shim is a hand-crafted RBI file that tells Sorbet about constants, ancestors, methods, etc. that it can’t understand statically and aren’t already generated by Tapioca.