make it optional to change the gene name to lower case

tutorial_tangram_without_squidpy.ipynb

@@ -444,7 +444,7 @@
     "- Also, the gene order needs to be the same in the datasets. This is because Tangram maps using only gene expression, so the $j$-th column in each matrix must correspond to the same gene.\n",
     "- And if data entries of a gene are all zero, this gene will be removed\n",
     "- This task is performed by the helper `pp_adatas`.\n",
-    "- if the gene names in single cell and spatial transcriptomics data are different due to inconsistent capitalization, we can set in the tg.pp_adatas function gene_to_lowercase = True to convert the whole name to the lower case"
+    "- In the pp_adatas function, the gene names are converted to lower case to get rid of the inconsistent capitalization. If the gene names in single cell and spatial transcriptomics data are different due to inconsistent capitalization, we can set in the tg.pp_adatas function gene_to_lowercase = True to convert the whole name to the lower case"
    ]
   },
   {