update main README

README.md

@@ -14,7 +14,7 @@ In this modified Cell Painting, there are three channels:
 There are two genotypes of the NF1 gene in these cells:
 
 - Wild type (`WT +/+`): In column 6 from the plate (e.g C6, D6, etc.)
-- Null (`Null`): In column 7 from the plate (e.g C7, D7, etc.)
+- Null (`Null -/-`): In column 7 from the plate (e.g C7, D7, etc.)
 
 It is important to study Schwann cells from NF1 patients because NF1 causes patients to develop neurofibromas, which are red bumps on the skin (tumors) that appear due to the loss of Ras-GAP neurofibromin. 
 This loss occurs when the NF1 gene is mutated (NF1 +/-).