Update README.md

Categorical heatmaps/README.md

+**UPDATE**: a more complex and versatile online alternative of this tool, for beautiful and configurable heatmaps is [Morpheus](https://software.broadinstitute.org/morpheus/).
+
 The script `generate_heatmap.R` can be used to represent a table of data in the form of an adjusted heat map. It uses two packages that need to be installed, `ggplot2` and `reshape2`. The input of the script is a tab delimited file text that looks like this:
 
 ![alt input table](./inputtable.png)
@@ -15,4 +17,4 @@ What the script does:
 [output]: ./heatplotexampleoutput.png
 
 
-The final results can be further enhanced and modified in Inkscape or Adobe illustrator.
\ No newline at end of file
+The final results can be further enhanced and modified in Inkscape or Adobe illustrator.