nichenetr and multinichenetr packages addendum of MultiNicheNet paper

Ligand-Treatment datasets for NicheNet-v2 model evaluation (nichenetr package vignette) Subsetted scRNA-seq datasets (SingleCellExperiment objects) for the several multinichenetr package vignettes用于NicheNet-v2模型评估的配体处理数据集（Ligand-Treatment datasets），配套来自nichenetr软件包的vignette文档；经子集化处理的单细胞RNA测序（single-cell RNA sequencing, scRNA-seq）数据集（SingleCellExperiment对象），可用于多个multinichenetr软件包的vignette文档。