Documentation for Lean Version Upgrade

[agureev]

Since Yatima is not currently in active development, it would be great to have documentation on how to upgrade the Lean version of the current project so that user may be able to still use compiler as the lake upgrade command suggested after lake run setup does not seem to bump everything properly.

Currently after pulling main and running lake run setup produces

warning: improperly formatted manifest: incompatible manifest version `4`
error: dependency 'LSpec' of 'Yatima' not in manifest, use `lake update` to update

while running lake update produces

warning: improperly formatted manifest: incompatible manifest version `4`
error: ./lake-packages/YatimaStdLib/lakefile.lean:14:15: error: invalid field 'oleanDir', the environment does not contain 'Lake.Package.oleanDir'
  pkg
has type
  Package
error: ./lake-packages/YatimaStdLib/lakefile.lean:23:33: error: unknown identifier 'defaultLibDir'
error: ./lake-packages/YatimaStdLib/lakefile.lean:23:57: error: application type mismatch
  List.cons job
argument
  job
has type
  CustomData (Package.name pkg, `importTarget) : Type
but is expected to have type
  BuildJob FilePath : Type
error: ./lake-packages/YatimaStdLib/lakefile.lean: package configuration has errors

Might be an issue with Lean4 Arch (AUR) package, however.