Add example data

Categorical heatmaps/data.txt

+Gene	Cell1	Cell2	Cell3	Cell4	Cell5	Cell6
+Gene1	506.105	494.267	503.205	706.487	556.187	590.515
+Gene2	164.432	171.984	111.435	382.903	354.203	204.256
+Gene3	563.404	600.591	914.213	957.619	614.368	1568.78
+Gene4	380.055	280.113	1182.2	2277.52	3205.36	3286.81
+Gene5	1194.75	1113.32	1055.19	1272.08	1360.91	1185.69
+Gene6	1371.78	1119.26	882.532	1518.3	850.484	1019.52
+Gene7	1426.41	1547.32	1876.36	1633.19	1715.85	1838.88
+Gene8	1271.25	714.69	1139.89	2147.23	1002.34	2462.07
+Gene9	768.371	793.149	1324.59	1135.57	1003.91	1898.04
+Gene10	33.1245	40.9437	39.1504	41.3754	95.4047	124.078
+Gene11	209.687	392.186	319.128	1203.81	491.908	2748.71
+Gene12	52.4478	58.6882	66.2085	92.661	237.715	71.8956
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