doc(tmp/lean4): expand explicit reference counter section
doc(tmp/lean4): expand explicit reference counter section

leodemoura/lean,digama0/lean,Kha/lean,Kha/lean,fpvandoorn/lean,fpvandoorn/lean,leodemoura/lean,dselsam/lean,leodemoura/lean,leanprover-community/lean,leodemoura/lean,fpvandoorn/lean,dselsam/lean,leanprover/lean,leanprover-community/lean,leanprover/lean,leanprover-community/lean,fpvandoorn/lean,dselsam/lean,digama0/lean,dselsam/lean,Kha/lean,fpvandoorn/lean,leanprover/lean,leanprover-community/lean,Kha/lean,leodemoura/lean,leanprover-community/lean,digama0/lean,dselsam/lean,leodemoura/lean,Kha/lean,leanprover/lean,digama0/lean,digama0/lean,dselsam/lean,digama0/lean,leanprover-community/lean,leanprover/lean,leanprover/lean,Kha/lean,fpvandoorn/lean